Real-Time Quantitative PCR To Determine Chlamydial Load in Men and Women in a Community Setting

We used a PCR method to quantify the loads of Chlamydia trachomatis organisms in self-collected urine and vulvovaginal swab (VVS) samples from 93 women and 30 men participating in the Chlamydia Screening Studies Project, a community-based study of individuals not seeking health care. For women, self-collected VVS had a higher mean chlamydial load (10,405 organisms/ml; 95% confidence interval [95% CI], 5,167 to 21,163 organisms/ml) than did first-void urines (FVU) (503 organisms/ml; 95% CI, 250 to 1,022 organisms/ml; P < 0.001). Chlamydial loads in female and male self-collected FVU specimens were similar (P = 0.634). The mean chlamydial load in FVU specimens decreased with increasing age in females and males. There was no strong statistical evidence of differences in chlamydial load in repeat male and female FVU specimens taken when patients attended for treatment a median of 23.5 (range, 14 to 62) and 28 (range, 13 to 132) days later, respectively, or in VVS taken a median of 35 (range, 14 to 217) days later. In this study, chlamydial load values for infected persons in the community who were not seeking treatment were lower than those published in other studies involving symptomatic patients attending clinical settings. This might have implications for estimates of the infectiousness of chlamydia. The results of this study provide a scientific rationale for preferring VVS to FVU specimens from women.Nucleic acid amplification tests to detect Chlamydia trachomatis have revolutionized the diagnosis and management of this common treatable sexually transmitted infection (6). Increased test sensitivity has enabled the use of noninvasive specimens, such as first-void urine specimens for men and women and vulvovaginal swabs for women, thus dispensing with the need for a genital examination and making it easier to perform screening tests on people without symptoms suggestive of chlamydial infection.The burden of C. trachomatis organisms in the genital tract (chlamydial load) can vary from 10 to over a million organisms per milliliter of genital tract secretions (4, 8). This is likely to influence the performance of different nucleic acid amplification tests, which do not routinely distinguish between people with high and low chlamydial loads (4, 8). Differences in chlamydial load have been reported to be associated with the presence of clinical symptoms (2, 8), the transmissibility and persistence of infection (3, 10), and the risk of developing chronic sequelae (2). Studies investigating the relevance of chlamydial load so far have been conducted only with patients attending health care settings (2, 4, 8). The objectives of this study were to measure chlamydial loads in individuals in a community setting and to investigate factors associated with chlamydial load.     

Variation in Susceptibility of Bloodstream Isolates of Candida glabrata to Fluconazole According to Patient Age and Geographic Location in the United States in 2001 to 2007

We examined the susceptibilities to fluconazole of 642 bloodstream infection (BSI) isolates of Candida glabrata and grouped the isolates by patient age and geographic location within the United States. Susceptibility of C. glabrata to fluconazole was lowest in the northeast region (46%) and was highest in the west (76%). The frequencies of isolation and of fluconazole resistance among C. glabrata BSI isolates were higher in the present study (years 2001 to 2007) than in a previous study conducted from 1992 to 2001. Whereas the frequency of C. glabrata increased with patient age, the rate of fluconazole resistance declined. The oldest age group (≥80 years) had the highest proportion of BSI isolates that were C. glabrata (32%) and the lowest rate of fluconazole resistance (5%).Candidemia is without question the most important of the invasive mycoses (6, 33, 35, 61, 65, 68, 78, 86, 88). Treatment of candidemia over the past 20 years has been enhanced considerably by the introduction of fluconazole in 1990 (7, 10, 15, 28, 29, 31, 40, 56-58, 61, 86, 90). Because of its widespread usage, concern about the development of fluconazole resistance among Candida spp. abounds (2, 6, 14, 32, 47, 53, 55, 56, 59, 60, 62, 80, 86). Despite these concerns, fluconazole resistance is relatively uncommon among most species of Candida causing bloodstream infections (BSI) (5, 6, 22, 24, 33, 42, 54, 56, 65, 68, 71, 86). The exception to this statement is Candida glabrata, of which more than 10% of BSI isolates may be highly resistant (MIC ≥ 64 μg/ml) to fluconazole (6, 9, 15, 23, 30, 32, 36, 63-65, 71, 87, 91). Suboptimal fluconazole dosing practices (low dose [<400 mg/day] and poor indications) may lead to an increased frequency of isolation of C. glabrata as an etiological agent of candidemia in hospitalized patients (6, 17, 29, 32, 35, 41, 47, 55, 60, 68, 85) and to increased fluconazole (and other azole) resistance secondary to induction of CDR efflux pumps (2, 11, 13, 16, 43, 47, 50, 55, 69, 77, 83, 84) and may adversely affect the survival of treated patients (7, 10, 29, 40, 59, 90). Among the various Candida species, C. glabrata alone has increased as a cause of BSI in U.S. intensive care units since 1993 (89). Within the United States, the proportion of fungemias due to C. glabrata has been shown to vary from 11% to 37% across the different regions (west, midwest, northeast, and south) of the country (63, 65) and from <10% to >30% within single institutions over the course of several years (9, 48). It has been shown that the prevalence of C. glabrata as a cause of BSI is potentially related to many disparate factors in addition to fluconazole exposure, including geographic characteristics (3, 6, 63-65, 71, 88), patient age (5, 6, 25, 35, 41, 42, 48, 63, 82, 92), and other characteristics of the patient population studied (1, 32, 35, 51). Because C. glabrata is relatively resistant to fluconazole, the frequency with which it causes BSI has important implications for therapy (21, 29, 32, 40, 41, 45, 56, 57, 59, 80, 81, 86, 90).Previously, we examined the susceptibilities to fluconazole of 559 BSI isolates of C. glabrata and grouped the isolates by patient age and geographic location within the United States over the time period from 1992 to 2001 (63). In the present study we build upon this experience and report the fluconazole susceptibilities of 642 BSI isolates of C. glabrata collected from sentinel surveillance sites throughout the United States for the time period from 2001 through 2007 and stratify the results by geographic region and patient age. The activities of voriconazole and the echinocandins against this contemporary collection of C. glabrata isolates are also reported.     

Characterization of a Campylobacter jejuni VirK Protein Homolog as a Novel Virulence Determinant

Campylobacter jejuni is a leading cause of food-borne illness in the United States. Despite significant recent advances, its mechanisms of pathogenesis are poorly understood. A unique feature of this pathogen is that, with some exceptions, it lacks homologs of known virulence factors from other pathogens. Through a genetic screen, we have identified a C. jejuni homolog of the VirK family of virulence factors, which is essential for antimicrobial peptide resistance and mouse virulence.Campylobacter jejuni is a leading cause of infectious diarrhea in industrialized and developing countries (2, 67). Although most often self-limiting, C. jejuni infections can also lead to severe disease and harmful sequelae, such as Guillain-Barré syndrome (4, 55). Despite the significant progress made during the past few years, the mechanisms of C. jejuni pathogenesis remain poorly understood. A number of potential virulence factors have been identified, and in some cases, their role in virulence and/or colonization has been demonstrated in animal models of infection. For example, motility has been shown to be crucial in order for C. jejuni to colonize or cause disease in several animal models of infection (1, 15, 30, 54). A variety of surface structures, such as adhesins (34, 40, 64) and polysaccharides (5, 6), and glycosylation systems (38, 74), which presumably modify some of these surface structures, have also been shown to be important for infection. Additional studies have revealed the importance of specific metabolic pathways in C. jejuni growth both in vitro and within animals (16, 25, 31, 60, 76). The ability of C. jejuni to invade and survive within nonphagocytic cells has also been proposed to be an important virulence determinant (21, 41, 57, 58, 68, 75, 80).The available genome sequences of several C. jejuni strains have provided significant insight into C. jejuni physiology and metabolism (22, 32, 62, 63, 65). Remarkably, however, analysis of these C. jejuni genome sequences has revealed very few homologs of common virulence factors from other pathogens. A notable exception is the toxin CDT (cytolethal distending toxin), which is also encoded by several other important bacterial pathogens (36, 44, 45). In this paper we describe the identification of a transposon insertion mutant in C. jejuni 81-176, which results in increased susceptibility to antimicrobial peptides and a significant defect in the ability of the organism to cause disease in an animal model of infection. The insertion mutant was mapped to the CJJ81176_1087 open reading frame (Cj1069 in the C. jejuni NCT 11168 reference strain), which encodes a protein with very significant amino acid sequence similarity to the VirK (DUF535) family of virulence factors (13, 20, 56).     

Identification of a Variety of Staphylococcus Species by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

Whole-cell fingerprinting by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) in combination with a dedicated bioinformatic software tool (MALDI Biotyper 2.0) was used to identify 152 staphylococcal strains corresponding to 22 staphylococcal species. Spectra of the 152 isolates, previously identified at the species level using a sodA gene-based oligonucleotide array, were analyzed against the main spectra of 3,030 microorganisms. A total of 151 strains out of 152 (99.3%) were correctly identified at the species level; only one strain was identified at the genus level. The MALDI-TOF MS method revealed different clonal lineages of Staphylococcus epidermidis that were of either human or environmental origin, which suggests that the MALDI-TOF MS method could be useful in the profiling of staphylococcal strains. The topology of the dendrogram generated by the MALDI Biotyper 2.0 software from the spectra of 120 Staphylococcus reference strains (representing 36 species) was in general agreement with that inferred from the 16S rRNA gene-based analysis. Our findings indicate that the MALDI-TOF MS technology, associated with a broad-spectrum reference database, is an effective tool for the swift and reliable identification of Staphylococci.Most staphylococci are harmless and reside normally on the skin and mucous membranes of humans and other organisms (16, 22, 34). Staphylococcal strains are isolated from various food products in which they are involved in fermentation (18, 29). Staphylococcus species can cause a wide variety of diseases in humans and other animals (2, 22, 30-32, 35). S. aureus is a major pathogen in human infections (31). Several other Staphylococcus species have also been implicated in human infections, notably S. saprophyticus, S. epidermidis, S. lugdunensis, and S. schleiferi (4, 16, 31, 34). Coagulase-negative staphylococci (CoNS) have emerged as predominant pathogens in hospital-acquired infections (4, 16, 31, 34). One of the major challenges of daily diagnostic work is therefore to identify Staphylococcus species.Several manual and automated methods based on phenotypic characteristics have been developed for the identification of Staphylococci (12, 24). Unfortunately, these systems have their limitations, mostly due to phenotypic differences between strains from the same species (6, 10, 19, 21). Over the last 10 years, many genotypic methods based on the analysis of selected DNA targets have been designed for species-level identification of most common isolated CoNS (20, 26, 33). The sequence polymorphism of the sodA gene has significant discriminatory power (20) and allows the development of assays based on DNA chip technologies (“Staph array”) (8). Recently, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using protein “fingerprints” was used for the identification of microorganisms (1, 3, 5, 9, 11, 14, 25, 36). In the present study, we assessed the ability of the MALDI Biotyper system (Bruker Daltonique, Wissembourg, France) to identify Staphylococcus species of clinical and environmental origins previously identified by sodA gene-based oligonucleotide array (8).     

Hag Mediates Adherence of Moraxella catarrhalis to Ciliated Human Airway Cells

Moraxella catarrhalis is a human pathogen causing otitis media in infants and respiratory infections in adults, particularly patients with chronic obstructive pulmonary disease. The surface protein Hag (also designated MID) has previously been shown to be a key adherence factor for several epithelial cell lines relevant to pathogenesis by M. catarrhalis, including NCIH292 lung cells, middle ear cells, and A549 type II pneumocytes. In this study, we demonstrate that Hag mediates adherence to air-liquid interface cultures of normal human bronchial epithelium (NHBE) exhibiting mucociliary activity. Immunofluorescent staining and laser scanning confocal microscopy experiments demonstrated that the M. catarrhalis wild-type isolates O35E, O12E, TTA37, V1171, and McGHS1 bind principally to ciliated NHBE cells and that their corresponding hag mutant strains no longer associate with cilia. The hag gene product of M. catarrhalis isolate O35E was expressed in the heterologous genetic background of a nonadherent Haemophilus influenzae strain, and quantitative assays revealed that the adherence of these recombinant bacteria to NHBE cultures was increased 27-fold. These experiments conclusively demonstrate that the hag gene product is responsible for the previously unidentified tropism of M. catarrhalis for ciliated NHBE cells.Moraxella catarrhalis is a gram-negative pathogen of the middle ear and lower respiratory tract (29, 40, 51, 52, 69, 78). The organism is responsible for ∼15% of bacterial otitis media cases in children and up to 10% of infectious exacerbations in patients with chronic obstructive pulmonary disease (COPD). The cost of treating these ailments places a large financial burden on the health care system, adding up to well over $10 billion per annum in the United States alone (29, 40, 52, 95, 97). In recent years, M. catarrhalis has also been increasingly associated with infections such as bronchitis, conjunctivitis, sinusitis, bacteremia, pneumonia, meningitis, pericarditis, and endocarditis (3, 12, 13, 17-19, 24, 25, 27, 51, 67, 70, 72, 92, 99, 102-104). Therefore, the organism is emerging as an important health problem.M. catarrhalis infections are a matter of concern due to high carriage rates in children, the lack of a preventative vaccine, and the rapid emergence of antibiotic resistance in clinical isolates. Virtually all M. catarrhalis strains are resistant to β-lactams (34, 47, 48, 50, 53, 65, 81, 84). The genes specifying this resistance appear to be gram positive in origin (14, 15), suggesting that the organism could acquire genes conferring resistance to other antibiotics via horizontal transfer. Carriage rates as high as 81.6% have been reported for children (39, 104). In one study, Faden and colleagues analyzed the nasopharynx of 120 children over a 2-year period and showed that 77.5% of these patients became colonized by M. catarrhalis (35). These investigators also observed a direct relationship between the development of otitis media and the frequency of colonization. This high carriage rate, coupled with the emergence of antibiotic resistance, suggests that M. catarrhalis infections may become more prevalent and difficult to treat. This emphasizes the need to study pathogenesis by this bacterium in order to identify vaccine candidates and new targets for therapeutic approaches.One key aspect of pathogenesis by most infectious agents is adherence to mucosal surfaces, because it leads to colonization of the host (11, 16, 83, 93). Crucial to this process are surface proteins termed adhesins, which mediate the binding of microorganisms to human cells and are potential targets for vaccine development. M. catarrhalis has been shown to express several adhesins, namely UspA1 (20, 21, 59, 60, 77, 98), UspA2H (59, 75), Hag (also designated MID) (22, 23, 37, 42, 66), OMPCD (4, 41), McaP (61, 100), and a type 4 pilus (63, 64), as well as the filamentous hemagglutinin-like proteins MhaB1, MhaB2, MchA1, and MchA2 (7, 79). Each of these adhesins was characterized by demonstrating a decrease in the adherence of mutant strains to a variety of human-derived epithelial cell lines, including A549 type II pneumocytes and Chang conjunctival, NCIH292 lung mucoepidermoid, HEp2 laryngeal, and 16HBE14o-polarized bronchial cells. Although all of these cell types are relevant to the diseases caused by M. catarrhalis, they lack important aspects of the pathogen-targeted mucosa, such as the features of cilia and mucociliary activity. The ciliated cells of the respiratory tract and other mucosal membranes keep secretions moving out of the body so as to assist in preventing colonization by invading microbial pathogens (10, 26, 71, 91). Given this critical role in host defense, it is interesting to note that a few bacterial pathogens target ciliated cells for adherence, including Actinobacillus pleuropneumoniae (32), Pseudomonas aeruginosa (38, 108), Mycoplasma pneumoniae (58), Mycoplasma hyopneumoniae (44, 45), and Bordetella species (5, 62, 85, 101).In the present study, M. catarrhalis is shown to specifically bind to ciliated cells of a normal human bronchial epithelium (NHBE) culture exhibiting mucociliary activity. This tropism was found to be conserved among isolates, and analysis of mutants revealed a direct role for the adhesin Hag in binding to ciliated airway cells.     

Genetic Variants of Human Parvovirus B19 in South Africa: Cocirculation of Three Genotypes and Identification of a Novel Subtype of Genotype 1

Parvovirus B19 comprises three distinct genotypes (1, 2, and 3). The distribution of B19 genotypes has not before been examined in South Africa. Two hundred thirty-nine laboratory samples submitted to a diagnostic virology laboratory for parvovirus DNA detection were analyzed retrospectively. Of the 53 PCR-positive samples investigated, 40 (75.4%) were identified as genotype 1 by genotype-specific PCR or consensus NS1 PCR and sequencing and 3 (5.7%) as genotype 2 and 10 (18.9%) as genotype 3 by analysis of NS1 sequences. Furthermore, phylogenetic analysis identified two genotype 1 sequences which were distinct from the previously described genotypes 1A and 1B. Interestingly, a genotype 2 virus was detected in the serum of an 11-year-old child, providing evidence for its recent circulation. This is the first study to demonstrate the concurrent circulation of all three genotypes of B19 in South Africa and the provisional identification of a novel subtype of genotype 1. The implications of parvovirus B19 variation are discussed.Parvovirus B19 is a member of the genus Erythrovirus of the family Parvoviridae (32). Until 2005, parvovirus B19 and adeno-associated viruses in the genus Dependovirus were the only known parvoviruses to infect humans (35). Recently two novel human parvoviruses have been discovered, namely, PARV4 and human bocavirus, with the latter associated with respiratory tract infections and PARV4, as yet, an orphan virus (1, 10, 18).Parvovirus B19 targets erythroid progenitor cells, and infection in humans is associated with a spectrum of clinical manifestations ranging from the mild erythema infectiosum in children to pure red cell aplasia due to persistent infection in immunocompromised persons. Chronic anemia due to persistent parvovirus infection is not uncommonly seen in HIV-infected individuals, particularly where access to highly active antiretroviral therapy (HAART) is delayed (23).While most individuals experience transient infection in childhood, there is mounting evidence that the virus persists following acute infection in certain tissue types, including liver, synovium, and skin (8, 15, 17, 19, 20, 26, 25, 31). The persistence of B19 DNA in tissue is thought to be lifelong and of uncertain clinical significance (25, 26). Norja et al. have termed this persistence of viral DNA in tissues the “bioportfolio” and are now utilizing this information to determine the evolution and molecular epidemiology of the virus (25, 26).The genome of parvovirus B19 consists of a single strand of linear DNA of about 5,600 nucleotides which encodes three proteins of known function, the nonstructural protein NS1 and the two structural proteins viral protein 1 (VP1) and viral protein 2 (VP2) (6, 7). Genetic variation among B19 strains is very low, with <2% divergence across the genome; however, certain genes such as the VP1 unique region (VP1-u) gene have greater sequence variation (up to 4%) (11, 14). Recently, several strains with considerable sequence diversity were discovered, resulting in the identification of three distinct genetic clusters.Three genotypes of erythrovirus are now recognized. Parvovirus B19 is the prototype of genotype 1 and is responsible for the majority of human infections worldwide (30). Genotypes 2 and 3 display more than 10% nucleotide divergence compared to reference B19 strains (30). Genotype 2 (prototypes LaLi and A6) has been identified at very low frequency in viremic individuals in Europe, Brazil, and Vietnam (16, 21, 24, 29, 33). In central and northern Europe, genotype 2 DNA has been found at much higher frequency in tissue samples of older individuals, and it is believed to be an ancestral virus that circulated in humans in this region up to the 1970s but was replaced by genotype 1 (26). Genotype 3 (prototypes V9 and D91.1) has been identified in French and Brazilian patients as well as in blood donors from Ghana, where it is though to be endemic (4, 29, 30).In addition to the three main genotypes, two subgroups of genotype 1 strains in Vietnamese patients and two subgroups of genotype 3 strains from Ghana, Europe, and Brazil have been described (4, 27, 33). Recent studies show that parvovirus B19, in contrast to other DNA viruses, has an inherent rate of genetic drift similar to that of RNA viruses, which in part explains the observed diversity (25, 26).To our knowledge, there have been no publications reporting on the diversity of B19 strains in South Africa. Of major relevance to the diagnostic laboratory is that both commercial and “in-house” PCR assays may fail to detect variants due to mismatches at primer binding sites (2, 5, 16). Indeed, this study was prompted by the identification of a patient with classic parvovirus-induced pure red cell aplasia in which the viral sequence was not amplified by a genotype 1-specific PCR assay. The aim of this retrospective study was to reanalyze samples that had been submitted to our diagnostic virology laboratory for parvovirus investigation using an assay able to detect all known parvovirus genotypes, with a view to determining the distribution of parvovirus variants in South Africa.     

Protection of Sheep against Rift Valley Fever Virus and Sheep Poxvirus with a Recombinant Capripoxvirus Vaccine

Rift Valley fever (RVF) is an epizootic viral disease of sheep that can be transmitted from sheep to humans, particularly by contact with aborted fetuses. A capripoxvirus (CPV) recombinant virus (rKS1/RVFV) was developed, which expressed the Rift Valley fever virus (RVFV) Gn and Gc glycoproteins. These expressed glycoproteins had the correct size and reacted with monoclonal antibodies (MAb) to native glycoproteins. Mice vaccinated with rKS1/RVFV were protected against RVFV challenge. Sheep vaccinated with rKS1/RVFV twice developed neutralizing antibodies and were significantly protected against RVFV and sheep poxvirus challenge. These findings further document the value of CPV recombinants as ruminant vaccine vectors and support the inclusion of RVFV genes encoding glycoproteins in multivalent recombinant vaccines to be used where RVF occurs.Rift Valley fever (RFV) virus (RVFV) is a mosquito-borne member of the genus Phlebovirus, family Bunyaviridae. It is widely distributed in Africa, causing endemic and epidemic disease in both humans and livestock, including sheep, cattle, and goats. RVF was first described in Kenya and was shown to be caused by a filterable virus transmissible via blood (9). Acute RVF in lambs is characterized by fever and death within 24 to 48 h of being detected (43). Signs in adult sheep include fever, mucopurulent nasal discharge, hemorrhagic diarrhea, and abortion in pregnant ewes (43). RVFV can be transmitted from infected sheep to humans, particularly when humans are exposed to aborted sheep fetuses and blood.Attenuated live RVFV vaccines are available for use in livestock. A mutagen-attenuated RVFV vaccine induces protective immune responses in lambs and appears to be safe (25); however, other studies documented teratogenic effects on lambs from vaccinated pregnant ewes similar to those caused by the attenuated RVFV strain Smithburn (18). An inactivated RVFV vaccine induces neutralizing antibody responses in humans (33), and its use in sheep would not induce teratogenic effects or abortions. However, the inactivated vaccine requires 3 doses (33) and is expensive to produce. Efforts to make RVFV vaccines without these disadvantages include an attenuated RVFV developed by reverse genetics and lacking the NSs and NSm genes (4) and other new-generation RVFV vaccines (reviewed in reference 19) that protect mice against virus challenge (7, 16, 24, 27).The middle (M) RNA segment of the RVFV genome encodes the viral glycoproteins Gn and Gc (8, 20), and recombinant vaccinia virus expressing these glycoproteins induces neutralizing antibody and protective immunity to RVFV in mice (7). Vaccinia virus is safe for animals, but there is some risk to humans, as it was reported previously to spread from human vaccinees to contacts (28, 55) and to cause serious clinical disease in human immunodeficiency virus-infected patients (36). Although modified vaccinia virus Ankara is a safer alternative for humans (6, 57), there are animal poxviruses with naturally restricted host ranges for vaccine vectors in animals (1, 13, 30, 31, 40, 46, 47, 52, 53).For ruminants, the genus Capripoxvirus (CPV) of the family Poxviridae has been an effective recombinant vector to induce protective immunity against several other viruses (3, 17, 29, 32, 40, 41, 51). This genus has three closely related species causing sheep pox, goat pox, and lumpy skin disease (LSD) of cattle. A recombinant LSD vaccine expressing the Gn and Gc glycoproteins of RVFV induced protection against RVFV challenge in mice (52, 53) and sheep (52). The three species of CPV have 96 to 97% nucleotide identity (49) and are restricted to ruminants, with no evidence of human infections (10, 11). Furthermore, attenuated CPV vaccines are in use in Africa and the Middle East to control ruminant poxvirus disease (11, 21). The use of a CPV vector to deliver virus vaccines to ruminants also induces immunity to the CPV vector, thus increasing the valence of the vaccine (3, 17, 39, 40). We report here the construction of a recombinant CPV that expresses the RVFV Gn and Gc glycoproteins and induces protective immunity against RVFV and sheep poxvirus (SPV) challenge in sheep.     

Acanthamoeba culbertsoni Elicits Soluble Factors That Exert Anti-Microglial Cell Activity

Acanthamoeba culbertsoni is an opportunistic pathogen that causes granulomatous amoebic encephalitis (GAE), a chronic and often fatal disease of the central nervous system (CNS). A hallmark of GAE is the formation of granulomas around the amoebae. These cellular aggregates consist of microglia, macrophages, lymphocytes, and neutrophils, which produce a myriad of proinflammatory soluble factors. In the present study, it is demonstrated that A. culbertsoni secretes serine peptidases that degrade chemokines and cytokines produced by a mouse microglial cell line (BV-2 cells). Furthermore, soluble factors present in cocultures of A. culbertsoni and BV-2 cells, as well as in cocultures of A. culbertsoni and primary neonatal rat cerebral cortex microglia, induced apoptosis of these macrophage-like cells. Collectively, the results indicate that A. culbertsoni can apply a multiplicity of cell contact-independent modes to target macrophage-like cells that exert antiamoeba activities in the CNS.Acanthamoeba culbertsoni belongs to a group of free-living amoebae, such as Balamuthia mandrillaris, Naegleria fowleri, and Sappinia pedata, that can cause disease in humans (46, 56). Acanthamoeba spp. are found worldwide and have been isolated from a variety of environmental sources, including air, soil, dust, tap water, freshwater, seawater, swimming pools, air conditioning units, and contaminated contact lenses (30). Trophozoites feed on bacteria and algae and represent the infective form (47, 56). However, under unfavorable environmental conditions, such as extreme changes in temperature or pH, trophozoites transform into a double-walled, round cyst (22, 45).Acanthamoeba spp. cause an infection of the eye known as amoebic keratitis (AK), an infection of the skin referred to as cutaneous acanthamoebiasis, and a chronic and slowly progressing disease of the central nervous system (CNS) known as granulomatous amoebic encephalitis (GAE) (22, 23, 30, 56). GAE is most prevalent in humans who are immunocompromised (30, 33, 40) and has been reported to occur among individuals infected with the human immunodeficiency virus (HIV) (28). It has been proposed that Acanthamoeba trophozoites access the CNS by passage through the olfactory neuroepithelium (32) or by hematogenous spread from a primary nonneuronal site of infection (23, 24, 33, 53).In immune-competent individuals, GAE is characterized by the formation of granulomas. These cellular aggregates consist of microglia, macrophages, polymorphonuclear cells, T lymphocytes, and B lymphocytes (24, 30). The concerted action of these immune cells results in sequestration of amoebae and is instrumental in slowing the progression of GAE. This outcome is consistent with the observation that granulomas are rarely observed in immunocompromised individuals (34) and in mice with experimentally induced immune suppression following treatment with the cannabinoid delta-9-tetrahydrocannabinol (Δ⁹-THC) (8).Microglia are a resident population of macrophages in the CNS. These cells, along with CNS-invading peripheral macrophages, appear to play a critical early effector role in the control of Acanthamoeba spread during GAE (4, 5, 29, 31). In vitro, microglia have been shown to produce an array of chemokines and cytokines in response to Acanthamoeba (31, 51). However, these factors appear not to have a deleterious effect on these amoebae (29).Acanthamoeba spp. produce serine peptidases, cysteine peptidases, and metallopeptidases (1, 2, 9, 10, 14, 16, 18, 19, 21, 25, 26, 37, 38, 41, 42, 52). In the present study, it is demonstrated that serine peptidases secreted by A. culbertsoni degrade chemokines and cytokines that are produced by immortalized mouse BV-2 microglia-like cells. In addition, soluble factors present in cocultures of A. culbertsoni and BV-2 cells induced apoptosis of the BV-2 cells. Collectively, these results suggest a mode through which A. culbertsoni can evade immune responsiveness in the CNS.     

Borrelia burgdorferi BmpA Is a Laminin-Binding Protein

The Borrelia burgdorferi BmpA outer surface protein plays a significant role in mammalian infection by the Lyme disease spirochete and is an important antigen for the serodiagnosis of human infection. B. burgdorferi adheres to host extracellular matrix components, including laminin. The results of our studies indicate that BmpA and its three paralogous proteins, BmpB, BmpC, and BmpD, all bind to mammalian laminin. BmpA did not bind mammalian type I or type IV collagens or fibronectin. BmpA-directed antibodies significantly inhibited the adherence of live B. burgdorferi to laminin. The laminin-binding domain of BmpA was mapped to the carboxy-terminal 80 amino acids. Solubilized collagen inhibited BmpA-laminin binding, suggesting interactions through the collagen-binding domains of laminin. These results, together with previous data, indicate that BmpA and its paralogs are targets for the development of preventative and curative therapies for Lyme disease.Early during the course of Lyme disease, humans frequently produce antibodies directed against a Borrelia burgdorferi antigen originally described as “P39” (66). Antibodies recognizing P39 are considered to be specific and diagnostic for Lyme disease spirochete infection (5, 18, 30, 62, 64). The antigenic protein was subsequently identified as BmpA (Borrelia membrane protein A) (65). The bmpA gene is located on the main borrelial chromosome, adjacent to three paralogous genes named bmpB, bmpC, and bmpD, which together form a complex operon (3, 4, 28, 32, 55, 56, 65). These other Bmp proteins are also often antigenic in infected humans (14). In addition to the serological data described above, examination of B. burgdorferi within skin and joint tissues confirmed the production of BmpA protein during mammalian infection (21, 49). BmpA is located in the borrelial outer membrane (46), where it is exposed to the external environment and can be a target of bactericidal antibodies (49, 63; F. Cabello, personal communication). BmpA and its paralogs have been implicated as playing roles in some symptoms of Lyme disease (49, 72). B. burgdorferi mutants in which bmpA or bmpB is specifically deleted are unable to persist in mouse joint tissues (49), indicating an important role for these proteins in the maintenance of mammalian infection. Despite the extensive research conducted on these important antigens, functions for the Bmp proteins had not been determined previously.B. burgdorferi is an extracellular organism, frequently found associated with its hosts'' connective tissues (6-9, 16, 17, 24, 26, 31, 36, 39, 48). In the laboratory, B. burgdorferi shows affinity for various host extracellular matrix (ECM) components, such as type I collagen, fibronectin, and decorin (16, 33, 34, 50, 74). We recently determined that B. burgdorferi also adheres to mammalian laminin, an important component of many mammalian ECMs (13). Ligand affinity blot analyses of a B. burgdorferi cell fraction enriched for outer membrane components revealed that the type strain, B31, can produce several distinct laminin-binding proteins, one of which we previously identified as being the surface-exposed outer membrane lipoprotein ErpX (11, 13, 69). We now present data indicating that BmpA and its paralogs are also laminin-binding proteins.     

Development of a Bead Immunoassay To Measure Vi Polysaccharide-Specific Serum IgG after Vaccination with the Salmonella enterica Serovar Typhi Vi Polysaccharide

Vi polysaccharide from Salmonella enterica serotype Typhi is used as one of the available vaccines to prevent typhoid fever. Measurement of Vi-specific serum antibodies after vaccination with Vi polysaccharide by enzyme-linked immunosorbent assay (ELISA) may be complicated due to poor binding of the Vi polysaccharide to ELISA plates resulting in poor reproducibility of measured antibody responses. We chemically conjugated Vi polysaccharide to fluorescent beads and performed studies to determine if a bead-based immunoassay provided a reproducible method to measure vaccine-induced anti-Vi serum IgG antibodies. Compared to ELISA, the Vi bead immunoassay had a lower background and therefore a greater signal-to-noise ratio. The Vi bead immunoassay was used to evaluate serum anti-Vi IgG in 996 subjects from the city of Kolkata, India, before and after vaccination. Due to the location being one where Salmonella serotype Typhi is endemic, approximately 45% of the subjects had protective levels of anti-Vi serum IgG (i.e., 1 μg/ml anti-Vi IgG) before vaccination, and nearly 98% of the subjects had protective levels of anti-Vi serum IgG after vaccination. Our results demonstrate that a bead-based immunoassay provides an effective, reproducible method to measure serum anti-Vi IgG responses before and after vaccination with the Vi polysaccharide vaccine.Typhoid fever is caused by Salmonella enterica serotype Typhi (32). Humans are the only natural host and reservoir of S. enterica serotype Typhi (32, 41). Typhoid fever represents a spectrum of diseases ranging from an acute uncomplicated disease—including fever, headache, malaise, and disturbances of bowel function (constipation in adults and diarrhea in children)—to a more severe, complicated form of disease in 10 to 20% of infected patients that includes bleeding in the gastrointestinal tract, intestinal perforation (in 1 to 3% of hospital typhoid fever cases) and an altered mental state (32, 41). The case fatality rate is highly variable, depending on the medical treatment available and geographic location. For example, the average fatality rate is less than 1% overall but may range between 2% fatality in hospitalized patients in Pakistan and Vietnam and 50% fatality in hospitalized patients in some parts of Indonesia and Papua New Guinea (32, 41). Worldwide, typhoid fever remains a significant public health problem, with an estimated 17,000,000 cases of typhoid fever each year and up to 600,000 deaths (2, 10, 32, 41).Typhoid vaccines currently available are composed of purified Vi polysaccharide or live attenuated S. enterica serotype Typhi (Ty21a) organisms (10, 39). The Vi polysaccharide vaccine induces protective serum antibody responses that reach a maximum at 28 days after a single intramuscular vaccination with 25 μg purified Vi polysaccharide (39), a capsular polysaccharide (Vi for virulence) that increases the virulence of S. enterica serotype Typhi (32). Protective antibody levels have been estimated to be 1 μg/ml anti-Vi IgG antibody in the serum (20). Protective efficacy of the Vi polysaccharide vaccine as determined by protection against disease is modest, with only 55 to 72% of subjects protected against disease through 3 years postvaccination (1, 20, 39). The live attenuated Ty21a vaccine is administered orally as three or four doses of enteric capsules (39). Due to its use as an oral, mucosally administered vaccine, the Ty21a vaccine induces protection against typhoid fever by induction of mucosal IgA and serum IgG antibodies specific for lipopolysaccharide antigens (39). The protective efficacy of the Ty21a vaccine at 3 years postvaccination was reported to range from 42 to 67% when using three doses of Ty21a enteric capsules (11, 39). Next-generation vaccines that utilize Vi conjugated to protein carriers that provide superior induction of anti-Vi antibodies are currently in development (14, 21, 25, 36).Despite its ability to induce protective immune responses when used alone or conjugated to protein carriers, the use of Vi polysaccharide as a coating antigen in enzyme-linked immunosorbent assay (ELISA) to measure vaccine-induced anti-Vi antibody responses has been reported to be problematic. The use of polysaccharides (lipopolysaccharide [LPS], Haemophilus influenzae type b capsular polysaccharide, Vi polysaccharide) as coating antigens for immunoassays is plagued by problems such as a poor binding of polysaccharides to ELISA plates and inconsistent results (3, 15, 16, 26, 33). To increase binding of Vi antigen to ELISA plates and produce more-robust assays, others have biotinylated Vi and then added it to streptavidin-coated plates (12) or conjugated Vi to tyramine (22, 26). However, some reports indicate that Vi was used without any additional treatment as an ELISA coating antigen (7, 19, 21) although a Vi ELISA performed on plates was less sensitive than a radioimmunoassay procedure (19).Immunoassays based on the use of fluorescent beads as the solid surface have recently been developed and compared to ELISA for the measurement of antigen-specific antibodies for polysaccharides from Streptococcus pneumoniae, Neisseria meningitidis, or Haemophilus influenzae type b (HiB) (5, 8, 23, 27, 34, 35). The fluorescent bead assays were comparable to ELISA and sometimes were noted as having enhanced dynamic ranges or increased sensitivity (5, 8, 27, 35). An additional benefit of fluorescent bead immunoassays is their ability to be multiplexed to permit the simultaneous measurement of antibodies specific for different antigens (8, 23, 27, 34, 35). This study was performed to evaluate a fluorescent bead immunoassay for its ability to measure vaccine-induced antibodies specific for Salmonella serotype Typhi Vi polysaccharide. The performance of the fluorescent bead assay was compared to that of ELISA.     

Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin Induces Apoptosis in Nonproliferating Macrophages by a Phosphatase-Independent Mechanism

Aggregatibacter actinomycetemcomitans strains that express cytolethal distending toxin (Cdt) are associated with localized aggressive periodontitis. However, the in vivo targets of Cdt in the human oral cavity have not been firmly established. Here, we demonstrate that A. actinomycetemcomitans Cdt kills proliferating and nonproliferating U937 monocytic cells at a comparable specific activity, approximately 1.5-fold lower than that against the Cdt-hypersensitive Jurkat T-cell line. Cdt functioned both as a DNase and a phosphatidylinositol 3-phosphate (PIP₃) phosphatase, and these activities were distinguished by site-specific mutagenesis of the active site residues of CdtB. Using these mutants, we determined that the DNase activity of CdtB is required for cell cycle arrest and caspase-dependent induction of apoptosis in proliferating U937 cells. In contrast, Cdt holotoxin induced apoptosis by a mechanism independent of caspase- and apoptosis-inducing factor in nonproliferating U937 cells. Furthermore, apoptosis of nonproliferating U937 cells was unaffected by the Cdt mutant possessing reduced phosphatase activity or by the addition of a specific PIP₃ phosphatase inhibitor, suggesting that the induction of apoptosis is independent of phosphatase activity. These results indicate that Cdt intoxication of proliferating and nonproliferating U937 cells occurs by distinct mechanisms and suggest that macrophages may also be potential in vivo targets of Cdt.Aggregatibacter (Actinobacillus) actinomycetemcomitans is associated with localized aggressive periodontitis (LAP) (40, 47, 48), a severe form of periodontal disease that results in the rapid destruction of the periodontal ligament and resorption of alveolar bone. Furthermore, growing evidence suggests that the oral cavity is a microbial reservoir for various systemic infections. In this regard, A. actinomycetemcomitans has also been associated with a variety of nonoral infections, including endocarditis, bacteremia, pericarditis, septicemia, pneumonia, infectious arthritis, osteomyelitis, synovitis, skin infections, urinary tract infections, and abscesses (45).Although A. actinomycetemcomitans expresses a variety of potential virulence factors, including epithelial cell adhesins (12, 13), an RTX leukotoxin (21, 23), and a cytolethal distending toxin (Cdt) (39, 41), their contributions to disease are not well understood. However, several studies suggest that Cdt may be important in the pathogenesis of LAP. For example, A. actinomycetemcomitans strains that possess the cdt operon are strongly associated with patients diagnosed with LAP (43). In addition, 97% of clinical A. actinomycetemcomitans isolates obtained from periodontitis patients in Sweden, Japan, Kenya, and Brazil possessed the cdt operon and were cytotoxic to CHO cells (10). In a separate study, Ahmed et al. (1) found that 86% of clinical A. actinomycetemcomitans isolates expressed Cdt and were toxic to HEp-2 cells.Cdt holotoxin is a tripartite complex comprised of subunits CdtA, CdtB, and CdtC (25, 33, 34). The CdtB protein is the active subunit and functions as a type I DNase (9, 24). However, a recent study shows that CdtB also functions as a phosphatidylinositol 3-phosphate (PIP₃) phosphatase and that many of the catalytic residues required for DNase activity are also necessary for phosphatase activity (36). CdtB is internalized by target cells, and internalization is inhibited by monensin, suggesting that entry occurs via the endocytic pathway (2). CdtA and CdtC are thought to interact with the target cell surface and may facilitate internalization of CdtB (2, 25, 27, 37). However, Mao and DiRienzo (27) suggest that both CdtB and CdtC are internalized by CHO cells and that CdtC may also possess toxic activity. CdtA is a putative lipoprotein that localizes to the bacterial outer membrane and is processed during secretion of the holotoxin (44).The in vivo cellular targets of the Cdt toxins are not well defined. Cdt holotoxin induces arrest in the G₂ phase of the cell cycle in a variety of proliferating cells, including epithelial cells, fibroblasts, human periodontal ligament cells, and lymphocytes (2, 3, 5, 8, 19, 20, 24, 25, 27, 28, 38, 41). Interestingly, Shenker et al. reported that the specific activity of Cdt against stimulated primary T lymphocytes was five- to 10-fold greater than that against HeLa cells (39) and subsequently showed that the Jurkat T-cell line is hypersensitive to Cdt intoxication (36). These results suggest that lymphocytes may be a primary physiologic target of the A. actinomycetemcomitans Cdt. Additional evidence that cells of the host immune response may be targeted by Cdt came from studies showing that purified Haemophilus ducreyi or Campylobacter jejuni Cdt induced apoptosis in nonproliferating dendritic cells (DCs) and macrophages (16, 26, 42, 46), although the specific activities against these cell types were not determined. Together, these studies suggest that many different cell types are potential targets of Cdt and that active proliferation may not be strictly required for Cdt intoxication.In this report, we show that A. actinomycetemcomitans Cdt induces apoptosis in both proliferating and nonproliferating U937 monocytic cells at a similar specific activity. Reconstituted Cdt holotoxin was shown to possess both DNase and PIP₃ phosphatase activities. Site-specific mutagenesis of CdtB active site residues generated one mutant with reduced DNase but significant phosphatase activity and a second mutant that was reduced in both activities. Cell cycle arrest and caspase 3-dependent induction of apoptosis in proliferating, nondifferentiated U937 cells were dependent on the DNase activity of CdtB. In contrast, Cdt-induced apoptosis in nonproliferating, differentiated U937 cells occurred by a mechanism independent of caspase- and apoptosis-inducing factor (AIF) and did not require a functional PIP₃ phosphatase activity. These results suggest that Cdt intoxication of proliferating and nonproliferating U937 cells occurs by distinct mechanisms and that macrophages may be potential in vivo targets of A. actinomycetemcomitans Cdt.     

Physical and Chemical Characterization and Immunologic Properties of Salmonella enterica Serovar Typhi Capsular Polysaccharide-Diphtheria Toxoid Conjugates

Typhoid fever remains a serious public health problem in developing countries, especially among young children. Recent studies showed more than 50% of typhoid cases are in children under 5 years old. Licensed vaccines, such as Salmonella enterica serovar Typhi capsular Vi, did not confer protection against typhoid fever for this age group. Vi conjugate, prepared by binding Vi to Pseudomonas aeruginosa recombinant exoprotein A (rEPA), induces protective levels of antibody at as young as 2 years old. Because of the lack of regulatory precedent for rEPA in licensing vaccines, we employed diphtheria toxoid (DT) as the carrier protein to accommodate accessibility in developing countries. Five lots of Vi-DT conjugates were prepared using adipic acid dihydrazide (ADH) as the linker. All 5 lots showed consistency in their physical and chemical characteristics and final yields. These Vi-DT conjugates elicited levels of IgG anti-Vi in young mice significantly higher than those in mice injected with Vi alone and induced a booster response upon reinjection. This booster effect was absent if the Vi replaced one of the two conjugate injections. Vi-DT was stable under repeated freeze-thaw (20 cycles). We plan to perform clinical evaluation of the safety and immunogenicity of Vi-DT when added to the infant combination vaccines.Typhoid fever, a serious systemic infection caused by Salmonella enterica serovar Typhi, remains a major public health problem in Central Asia, Southeast Asia, Africa, and Latin America (11, 52, 53). It was estimated that more than 21 million cases of typhoid fever and >200,000 deaths occurred in 2000 (10). The treatment of patients and management of asymptomatic carriers are becoming more difficult due to the worldwide emergence of multidrug-resistant (MDR) strains (2, 15, 29, 42, 43). Vaccination is considered the most promising strategy for the control of typhoid fever in developing countries (11, 19, 52, 53).Typhoid fever in children younger than 5 years old has often been unrecognized due to atypical clinical symptoms, difficulties in the number and volume of blood drawings, and use of less than optimal culture media (35, 46). Several studies have shown that the incidence of typhoid fever among children less than 5 years old is similar to that in school age children and young adults (14, 27, 34, 50, 51).The 3 licensed typhoid vaccines have limited efficacy, and none are suitable for young children under 5 years old. The use of heat-inactivated whole-cell vaccine was suspended in many countries because of its reactogenicity. The parenteral Vi polysaccharide and the live attenuated oral Ty21a vaccine were introduced in the late 1980s; both vaccines are well accepted and confer moderate protection (50 to 70%) in older children and adults. However, neither vaccine is licensed for routine immunization of infants (52).The Vi capsular polysaccharide is both an essential virulence factor and a protective antigen for S. Typhi (36, 38, 39). The concentration of serum IgG anti-Vi is correlated with immunity to the pathogen (22, 25, 26, 28, 36, 38, 49). However, Vi is not suitable for routine immunization of infants and young children because of its age-related immunogenicity and T-cell independence. As was shown for other capsular polysaccharides, such as Haemophilus influenzae type b (8, 37); meningococcus groups A, C, and W135; and Streptococcus pneumoniae (12, 20), Vi covalently bound with protein conferred T-cell dependence and increased immunogenicity (48-50). To date, diphtheria toxoid (DT), tetanus toxoid (TT), cholera toxins (CT), the B subunit of the heat-labile toxin (LT-B) of Escherichia coli, recombinant outer membrane protein of Klebsiella pneumoniae (rP40), and iron-regulated outer-membrane proteins (IROMPs) of S. Typhi have served as carriers for Vi polysaccharide in laboratory studies (16, 17, 32, 48-50; personal communications). An improved method was developed (24), utilizing adipic acid dihydrazide (ADH) as the linker and Pseudomonas aeruginosa recombinant exoprotein A (rEPA) as the carrier. Clinical trials of Vi-rEPA conjugates conferred 89% protection in Vietnamese children 2 to 5 years old for 46 months (23, 26, 28). The level of serum IgG anti-Vi induced by Vi-rEPA conjugates was correlated with prevention of typhoid fever in these studies (7, 21-23, 26, 28).One limitation of using rEPA as the carrier protein is the lack of regulatory precedent in licensing vaccines. In this report, five lots of Vi conjugates using DT manufactured by pharmaceutical companies in China and India were prepared (24, 48, 49). Modifications of conjugation procedures were made for the purposes of easy adoption and scale up by manufacturers. The stability of Vi-DT was studied for the feasibility of stockpiling in disaster relief.Another important aspect of conjugate vaccine implementation is the optimum immunization formulation and schedule using alternating injections of polysaccharide and conjugate. Priming or boosting effects of polysaccharide on its conjugate vaccine have been observed in infants injected with pneumococcal and meningococcal vaccines (3, 4, 31, 40). There was no consistent conclusion about various types of polysaccharides studied (6, 9, 31, 40, 41). Here, we compared the immune response of Vi polysaccharide injected before or after the administration of Vi-DT with the responses of those receiving 2 injections of Vi-DT. We also investigated the dosage effect for the purpose of better formulation.     

Development and Validation of a Multiplex Real-Time PCR Assay for Simultaneous Genotyping and Human T-Lymphotropic Virus Type 1, 2, and 3 Proviral Load Determination

The human T-lymphotropic virus (HTLV) proviral load remains the best surrogate marker for disease progression. Real-time PCR techniques have been developed for detection and quantification of cosmopolitan HTLV type 1a (HTLV-1a) and HTLV-2. Since a growing level of diversity in subtypes and genotypes is observed, we developed a multiplex quantitative PCR for simultaneous detection, genotyping, and quantification of proviral loads of HTLV-1, 2, and 3. Our assay uses tax type-specific primers and dually labeled probes and has a dynamic range of 10⁵ to 10 HTLV copies. One hundred sixty-three samples were analyzed, among which all of the different subtypes within each HTLV genotype could be detected. The performance of proviral load determination of our multiplex assay was compared with that of a previously published HTLV-1 singleplex quantitative PCR based on SYBR green detection, developed at a different institute. Linear regression analysis showed a statistically significant (P < 0.0001) and strong (r² = 0.87) correlation between proviral load values measured with the two distinct real-time PCR assays. In conclusion, our novel assay offers an accurate molecular diagnosis and genotyping, together with the determination of the proviral load of HTLV-infected individuals, in a single amplification reaction. Moreover, our molecular assay could offer an alternative when current available serological assays are insufficient.Since the discovery of human T-lymphotropic virus type 1 (HTLV-1) in 1980 (16, 40), three other genotypes and 10 subtypes have been recognized. The precise geographical distribution and the clinical consequences of these infections are still a matter of debate. This can be attributed at least in part to the fact that there are insufficient accurate tools for HTLV diagnosis, genotyping, and measurement of viral burden.HTLV-1 is endemic in several geographical areas, including sub-Saharan Africa, South America, the Caribbean Islands, Japan, and Melanesia. It has been estimated that worldwide 10 to 25 million people are infected with this retrovirus (41, 53). Most HTLV-1-infected individuals remain asymptomatic throughout their lifetimes. However, 5 to 10% of infected people develop clinical complications, among which adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) are the most severe. Other manifestations of HTLV-1 infection include infective dermatitis (25), uveitis (34), arthritis (38), and Strongyloides stercoralis infection (53). Some of these manifestations could accelerate disease development and/or progression (12, 16). For HTLV-1, a distinction is made between seven subtypes: the worldwide, cosmopolitan subtype HTLV-1a; the Central African subtypes HTLV-1b, -d, -e, -f, and -g; and the Australo-Melanesic subtype HTLV-1c (8, 23, 41, 52).HTLV-2 was discovered in 1982. This retrovirus is endemic in Amerindian and pygmy populations and epidemic in intravenous drug users (16, 49). In contrast to the case for HTLV-1, convincing epidemiological demonstrations of a definitive etiological role of HTLV-2 in human disease are limited. Nevertheless, HTLV-2 has been linked with the development of neurological disorders similar to HAM/TSP, with arthritis, with pulmonary disorders, and with increased mortality (2, 16, 42). HTLV-2 is divided into three subtypes, namely, HTLV-2a and HTLV-2b, mostly found on the American continent, and HTLV-2d, mostly found in Africa (10, 41, 44, 52).In 2005, two more genotypes, HTLV-3 and -4, were discovered in asymptomatic individuals from Cameroon (6, 7, 47, 56). To date, no diseases have been reported in association with HTLV-3 or -4. Further research is needed to determine the distribution and prevalence as well as the pathogenicity of these two new genotypes.The routine diagnosis of HTLV infections is based on conventional serological techniques such as enzyme-linked immunosorbent assay and Western blotting. However, among samples infected with HTLV-1 or HTLV-2, the proportion of seroindeterminate results is high (20, 21, 28, 57). Moreover, in the cases of HTLV-3 and HTLV-4, an indeterminate Western blot pattern appears to be the rule rather than the exception (6, 29). To confirm and/or support serological assays, diagnostic HTLV PCR techniques were created (51, 54). In the next phase, real-time or quantitative PCR (qPCR) assays were developed that confirm the diagnosis and at the same time quantify the HTLV proviral load (PVL). The majority of the published HTLV qPCR assays are singleplex assays, which detect one HTLV genotype per amplification reaction and hereby were developed for the most prevalent variant of HTLV-1, the cosmopolitan HTLV-1a, or for HTLV-2 infection (11, 22, 26, 32, 55). Multiplex qPCR allows the simultaneous detection and amplification of two or more target DNA sequences in only one amplification reaction. To our knowledge, one specific and one generic biplex qPCR for HTLV-1 and -2 (13, 26) and, just recently, one triplex qPCR for HTLV-1, -2, and -3 have been described (3).To address the current problems with HTLV diagnosis and quantitation, taking into account the diversity in HTLV genotypes and subtypes, we developed a novel triplex qPCR assay for simultaneous detection, genotyping, and quantification of PVL of HTLV-1, -2, and -3 infections. In the future, HTLV-4 can be incorporated into our qPCR technique, provided that viral cell culture is possible. Furthermore, considering the increasing number of HTLV qPCR techniques available at present, together with the lack of validation, we performed the first comparative analysis between two qPCR assays developed at different institutions.     

Growth in a Biofilm Induces a Hyperinfectious Phenotype in Vibrio cholerae

Biofilm formation plays a multifaceted role in the life cycles of a wide variety of microorganisms. In the case of pathogenic Vibrio cholerae, biofilm formation in its native aquatic habitats is thought to aid in persistence during interepidemic seasons and to enhance infectivity upon oral ingestion. The structure of V. cholerae biofilms has been hypothesized to protect the bacteria during passage through the stomach. Here, we directly test the role of biofilm architecture in the infectivity of V. cholerae by comparing the abilities of intact biofilms, dispersed biofilms, and planktonic cells to colonize the mouse small intestine. Not only were V. cholerae biofilms better able to colonize than planktonic cells, but the structure of the biofilm was also found to be dispensable: intact and dispersed biofilms colonized equally, and both vastly out-colonized planktonic cells. The infectious dose for biofilm-derived V. cholerae was orders of magnitude lower than that of planktonic cells. This biofilm-induced hyperinfectivity may be due in part to a higher growth rate of biofilm-derived cells during infection. These results suggest that the infectious dose of naturally occurring biofilms of V. cholerae may be much lower than previously estimated using cells grown planktonically in vitro. Furthermore, this work implies the existence of factors specifically induced during growth in a biofilm that augment infection by V. cholerae.Bacteria are often found in biofilms, surface-attached aggregates of microorganisms encased in an extracellular polysaccharide or protein matrix (14). Mature bacterial biofilms often assume a three-dimensional structure composed of pillars of bacteria separated by fluid-filled channels (15). Compared to their free-living, planktonic (PL) counterparts, biofilm-associated bacteria have been shown to be recalcitrant to a variety of stresses and antimicrobial agents, including chlorine, low pH, UV irradiation, antibiotics, host defenses, and more (4, 16, 21, 22, 39, 40, 44, 63, 72). The structure of the biofilm itself has been thought to physically protect the bacteria within. The decreased susceptibility of biofilms to antibiotics, for example, is understood to be due at least in part to decreased permeability of the biofilm to the antibiotic (20, 30, 60). However, growth rate and metabolic state have also been proposed to contribute to biofilm-related protection from certain antimicrobials and other stresses (5, 25, 59, 68). In addition, distinct genetic mechanisms of antibiotic resistance employed by biofilm microorganisms have been described (34, 41, 42).The ability to form biofilms is a virulence determinant of many microorganisms. Classic examples of biofilm infections include chronic infections of the cystic fibrosis lung by Pseudomonas aeruginosa, Haemophilus influenzae and Streptococcus pneumoniae in chronic otitis media, uropathogenic Escherichia coli in recurrent urinary tract infections, and disease caused by microbial biofilms on a variety of indwelling medical devices (27, 35, 36, 52, 56). The reduced susceptibility of in vivo biofilms to antimicrobials has a huge impact on human health due to the difficulty involved in their eradication.In other instances, biofilm formation contributes to a microorganism''s survival in an environmental niche, such as in water system piping or on other solid surfaces, and consequently affects the likelihood of contact with a host (24, 58, 69). Vibrio cholerae is the causative agent of cholera and is a natural inhabitant of freshwater, marine, and estuarine environments. In the aquatic environment, V. cholerae has been observed to form biofilms on abiotic and biotic surfaces, including those of zooplankton, phytoplankton, algae, and crustaceans (23, 33, 62). This surface-attached state is thought to be the primary means of persistence of V. cholerae in the environment, providing protection from a variety of stresses and, when the bacteria are attached to chitin, a source of nutrients and a forum for acquiring new genetic material (43, 45, 46, 50, 67, 71). Moreover, biofilms are likely a form in which pathogenic (toxigenic) V. cholerae is consumed by humans, and they provide a means by which humans can obtain a concentrated infective dose (13, 28, 32). Because chitin- and biofilm-associated V. cholerae is better able to survive acid exposure (50, 72), it has been hypothesized that V. cholerae biofilms are protected during transit through the gastric acid barrier of the stomach, thus allowing more bacteria to reach the small intestine colonization site. Yet the role of stomach acid in susceptibility to cholera is unclear in humans (26), and the infant mouse, with neutral pH in the stomach, may be an irrelevant model of this phenomenon.In this work, we test the hypothesis that the biofilm structure itself enhances colonization of the small intestine by V. cholerae. Instead, we found that V. cholerae bacteria dispersed from a biofilm are as infectious as those in an intact biofilm and that both are dramatically more infectious than free-living, planktonic cells in the infant mouse model. This work suggests that the physiological state of V. cholerae in biofilms, and not the biofilm structure, is the primary contributor to hyperinfectivity.     

Diagnosis of Bacteremia in Whole-Blood Samples by Use of a Commercial Universal 16S rRNA Gene-Based PCR and Sequence Analysis

In a prospective, multicenter study of 342 blood samples from 187 patients with systemic inflammatory response syndrome, sepsis, or neutropenic fever, a new commercial PCR test (SepsiTest; Molzym) was evaluated for rapid diagnosis of bacteremia. The test comprises a universal PCR from the 16S rRNA gene, with subsequent identification of bacteria from positive samples by sequence analysis of amplicons. Compared to blood culture (BC), the diagnostic sensitivity and specificity of the PCR were 87.0 and 85.8%, respectively. Considering the 34 BC-positive patients, 28 were also PCR positive in at least one of the samples, resulting in a patient-related sensitivity of 82.4%. The concordance of PCR and BC for both positive and negative samples was (47 + 247)/342, i.e., 86.0%. In total, 31 patients were PCR/sequencing positive and BC negative, in whom the PCR result was judged as possible or probable to true bacteremia in 25. In conclusion, the PCR approach facilitates the detection of bacteremia in blood samples within a few hours. Despite the indispensability of BC diagnostics, the rapid detection of bacteria by SepsiTest appears to be a valuable tool, allowing earlier pathogen-adapted antimicrobial therapy in critically ill patients.Bloodstream infection is a life-threatening condition with a high mortality rate, especially in intensive care and neutropenic patients (5, 19, 35, 38). Pathogenic bacteria are the most frequent causes of bloodstream infection, although fungi can also be isolated in a minority of patients (7, 17, 21, 32, 34). Currently, inoculation of blood cultures (BC) is the standard method for microbiological diagnosis of bloodstream infections. However, the limitations of BC include relatively low sensitivities and a long time-to-result for detection and identification of the pathogen, generally over 2 days, and even longer for fastidious organisms (13, 20, 27).In contrast, DNA-based procedures may offer faster and more reliable diagnoses (3, 30). PCR amplification of microbial genes, followed by detection of amplified products by gel electrophoresis or real-time PCR monitoring using fluorescent dyes or target-directed fluorescent probes, is a quick process allowing pathogen detection within a few hours (18). Identification of microorganisms can be performed by PCR algorithms, taxon-specific oligonucleotide microarrays, or sequencing amplicons (30).PCR amplification of conserved regions of the bacterial genome, in particular the 16S rRNA gene, combined with sequence analysis is a well-established technique for the identification of bacterial pathogens (18). The main advantages of targeting the 16S rRNA gene are the broad range of pathogens detectable and the independence of this method from the in vitro viability of strains (6). The high sensitivity of detection by PCR of bacterial DNA (15) suggests its use in the diagnosis of bacteremia (16). Initial disadvantages of PCR, notably the incidence of false-positive results from bacterial DNA contaminating PCR reagents (4, 39), have been counteracted by the development of purification methods (12, 28) and the availability of commercial products (22).We present here a prospective, multicenter study investigating blood samples from patients with suspected bloodstream infections by a new, commercial, universal 16S rRNA gene-based PCR assay (SepsiTest; Molzym, Bremen, Germany) combined with sequence analysis of the amplicon for the identification of pathogens. The results obtained were compared to standard BC diagnostics.     

Antibodies to Reticulocyte Binding Protein-Like Homologue 4 Inhibit Invasion of Plasmodium falciparum into Human Erythrocytes

Plasmodium falciparum invasion into human erythrocytes relies on the interaction between multiple parasite ligands and their respective erythrocyte receptors. The sialic acid-independent invasion pathway is dependent on the expression of P. falciparum reticulocyte binding protein-like homologue 4 (PfRh4), as disruption of the gene abolishes the ability of parasites to switch to this pathway. We show that PfRh4 is present as an invasion ligand in culture supernatants as a 160-kDa proteolytic fragment. We confirm that PfRh4 binds to the surfaces of erythrocytes through recognition of an erythrocyte receptor that is neuraminidase resistant but trypsin and chymotrypsin sensitive. Serum antibodies from malaria-exposed individuals show reactivity against the binding domain of PfRh4. Purified immunoglobulin G raised in rabbits against the binding domain of PfRh4 blocked the binding of native PfRh4 to the surfaces of erythrocytes and inhibited erythrocyte invasion of parasites using sialic acid-independent invasion pathways and grown in neuraminidase-treated erythrocytes. Our results suggest PfRh4 is a potential vaccine candidate.During the asexual stage of the Plasmodium falciparum life cycle, the parasite undergoes rapid replication within the erythrocytes of the human host, resulting in the clinical manifestations seen in malaria infections. The merozoite forms of P. falciparum invade erythrocytes through a multistep process that involves initial contact with the erythrocyte, apical reorientation of the merozoite, and the formation of a tight junction, which moves progressively toward the posterior end of the parasite until host cell membrane fusion is completed (for a review, see reference 9). These steps in invasion are dependent on specific interactions between multiple parasite invasion ligands and their respective host erythrocyte receptors (8, 20). Although P. falciparum has a very restricted host cell range, it has developed the ability to invade human erythrocytes using multiple parasite ligand-erythrocyte receptor interactions that have become known as alternative invasion pathways (11, 12, 14, 21, 31).Broadly speaking, there are two major invasion pathways in P. falciparum, one that is dependent on sialic acid (SA) residues, termed the SA-dependent pathway, and one that is independent of SA, called the SA-independent pathway (23, 30, 37, 38). SA moieties on the surfaces of erythrocytes can be removed by treatment with the enzyme neuraminidase. Parasite strains that invade neuraminidase-treated erythrocytes efficiently are called SA-independent strains, whereas strains that invade inefficiently into the treated erythrocytes are called SA-dependent strains. To date, two gene families encoding invasion ligands have been identified as major players in these invasion pathways: those encoding the erythrocyte binding antigens (EBAs) (EBA-175; EBA-181, also known as JESEBL; and EBA-140, also known as BAEBL) (2, 19, 26-28, 44, 48) and those encoding the P. falciparum reticulocyte binding protein-like homologues (PfRhs) (PfRh1, PfRh2a, PfRh2b, PfRh3, PfRh4, and PfRh5) (4, 14, 22, 24, 40, 41, 43, 46, 51). All members of these families are expressed and functional, except the EBA-165 (also known as PAEBL) and PfRh3 genes, which appear to be pseudogenes (47, 52). Previous studies have shown that the EBAs and PfRh1 are involved in the SA-dependent pathway, whereas PfRh2b and PfRh4 are important in the SA-independent pathway (14, 16, 18, 26, 27, 41, 42, 46, 50). Host receptors have been identified only for EBA-175 and EBA-140, which bind to glycophorin A and C, respectively (26, 27, 29, 44). Both EBA-181 and PfRh1 have been shown to bind SA on the erythrocyte surface, although the identities of these receptors are unknown (15, 19, 41). EBA181 has also been reported to bind band 4.1 (25).Changes in the expression and activation of some PfRhs enable the parasite to utilize alternate invasion pathways, and clinical P. falciparum isolates show diversity in invasion phenotypes and expression of EBA and PfRh proteins (5, 6, 10, 14, 16, 35, 46). For instance, W2mef parasites primarily invade via an SA-dependent pathway, using EBA-175 as a key invasion ligand (16, 46). In this strain, there is no detectable expression of PfRh4. Through a targeted knockout of EBA-175 or selection of W2mef for invasion of neuraminidase-treated erythrocytes, this strain has the ability to switch to an SA-independent invasion pathway (13, 42). The switch in invasion pathway is concurrent with an increase in PfRh4 protein expression (16, 46). PfRh4 is essential in the SA-independent pathway, as disruption of the gene in W2mef results in the inability of the strain to switch invasion pathways to allow invasion into neuraminidase-treated erythrocytes (46). The activation of PfRh4 in response to the loss of EBA-175 function suggests that the PfRh and EBA families overlap with respect to their functions in invasion (14, 46). Recent studies demonstrated that PfRh4 binds to the surfaces of erythrocytes (17). By varying the levels of expression of these invasion ligands, the parasite is able to switch receptor usage from SA-dependent to SA-independent pathways, providing a mechanism for the parasite to evade the host immune system (14, 39, 46). The ability to use different receptor-ligand interactions for invasion may also enable the parasites to adapt to different physiological conditions in different hosts.EBAs and PfRhs are located at the merozoite apical tip to allow recognition of and binding to their erythrocyte receptor (1, 14, 46). For successful parasite entry into the erythrocyte, the tight junction formed between these transmembrane parasite ligands and their receptors must be released. It is thought that this release occurs through the cleavage of invasion ligands by rhomboid proteases (3, 34, 54). Subsequently, these proteolytic fragments are shed into the bloodstream, resulting in parasite ligands being exposed to the human immune system. Therefore, although these ligands are crucial in the invasion process, it is also highly likely that EBAs and PfRhs are targets of inhibitory antibodies of the human immune system (39). Inhibitory antibodies are thought to be an important component of acquired protective immunity through their ability to block invasion by a parasite and its subsequent rapid replication within erythrocytes. In support of the importance of inhibitory antibodies, previous studies have shown that rabbit antibodies against EBA-175, EBA-140, PfRh2b, and PfRh1 inhibit parasite invasion in vitro (14, 15, 27, 41, 45). Differential inhibition by human antibodies of P. falciparum lines that vary in their use of specific EBA and PfRh proteins pointed to these ligand families as major targets of inhibitory antibodies (39).Although PfRh4 has an important role in the SA-independent pathway, antibodies generated against PfRh4 domains have shown no inhibition of merozoite invasion (17). A recombinant 30-kDa protein in a conserved region of PfRh4 (rRh4₃₀) has been shown to bind to erythrocytes in a neuraminidase-resistant, chymotrypsin- and trypsin-sensitive manner (17). Addition of rRh4₃₀ itself or anti-rRh4₃₀ antibodies into an erythrocyte binding assay resulted in the inhibition of native PfRh4 erythrocyte binding; however, these anti-rRh4₃₀ antibodies did not inhibit parasite invasion. In immunoblots, these antibodies detected PfRh4 as a 250-kDa protein in saponin-lysed schizont pellets, a protein size not consistent with other published reports (24, 46). Furthermore, a processed form of PfRh4 was not detected in culture supernatants using these antibodies, though others have suggested that PfRh4 is proteolytically cleaved and released into the culture supernatant by rhomboid proteases during the invasion process (3).In light of the importance of PfRh4 in parasite invasion, we examined the binding of PfRh4 to erythrocytes, evidence that PfRh4 is proteolytically processed, and the role of antibodies against PfRh4 in inhibition of erythrocyte invasion. Our work shows that recombinant PfRh4 reacts with sera from malaria-exposed individuals and that antibodies to it inhibit parasite invasion. This suggests that PfRh4, a major invasion ligand for the SA-independent pathway, is exposed to the human immune system and provides a target of inhibitory antibodies and is therefore a potential vaccine candidate.