Genetic Fusions of Heat-Labile (LT) and Heat-Stable (ST) Toxoids of Porcine Enterotoxigenic Escherichia coli Elicit Neutralizing Anti-LT and Anti-STa antibodies

Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of diarrheal disease in humans and farm animals. E. coli fimbriae, or colonization factor antigens (CFAs), and enterotoxins, including heat-labile enterotoxins (LT) and heat-stable enterotoxins (ST), are the key virulence factors in ETEC diarrhea. Unlike fimbriae or LT, STa has not often been included as an antigen in development of vaccines against ETEC diarrhea because of its poor immunogenicity. STa becomes immunogenic only after being coupled with a strongly immunogenic carrier protein. However, native or shorter STa antigens either had to retain toxic activity in order to become antigenic or elicited anti-STa antibodies that were not sufficiently protective. In this study, we genetically mutated the porcine LT (pLT) gene for a pLT_192(R→G) toxoid and the porcine STa (pSTa) gene for three full-length pSTa toxoids [STa_11(N→K), STa_12(P→F), and STa_13(A→Q)] and used the full-length pLT₁₉₂ as an adjuvant to carry the pSTa toxoid for pLT₁₉₂:pSTa-toxoid fusion antigens. Rabbits immunized with pLT₁₉₂:pSTa₁₂ or pLT₁₉₂:pSTa₁₃ fusion protein developed high titers of anti-LT and anti-STa antibodies. Furthermore, rabbit antiserum and antifecal antibodies were able to neutralize purified cholera toxin (CT) and STa toxin. In addition, preliminary data suggested that suckling piglets born by a sow immunized with the pLT₁₉₂:pSTa₁₃ fusion antigen were protected when challenged with an STa-positive ETEC strain. This study demonstrated that pSTa toxoids are antigenic when fused with a pLT toxoid and that the elicited anti-LT and anti-STa antibodies were protective. This fusion strategy could provide instructive information to develop effective toxoid vaccines against ETEC-associated diarrhea in animals and humans.Enterotoxigenic Escherichia coli (ETEC) strains, which colonize host small intestines and produce one or more enterotoxins, are the major cause of diarrheal disease in humans and farm animals. The virulence determinants of ETEC in diarrhea include fimbrial adhesins and enterotoxins (1, 6, 10, 27, 28, 37, 44, 48). Fimbrial adhesins mediate attachment of bacteria to host epithelium cells and facilitate subsequent bacteria colonization. Enterotoxins, including heat-stable enterotoxins (STa and STb) and heat-labile enterotoxins (LT) (19, 20, 35), disrupt intestinal fluid homeostasis and cause fluid and electrolyte hypersecretion through activation of adenyl cyclase (by LT) or guanylate cyclase (by STa) in small intestinal epithelial cells (21, 26). ETEC strains isolated from young pigs with diarrhea express LT, STa, STb, Stx2e, and enteroaggregative E. coli ST type 1 (EAST1), alone or combined (10, 15, 50). Recent experimental studies indicated that porcine ETEC strains expressing LT, STb, or STa alone are sufficiently virulent to cause diarrhea in young pigs (6, 48, 49).Porcine ETEC-associated diarrhea, especially postweaning diarrhea (PWD), causes a substantial economic loss to swine producers worldwide (18, 41). Currently, there are no vaccines available to effectively protect weaned pigs against ETEC infections. Experimental vaccines developed from fimbrial antigens alone showed only limited protection against ETEC strains (42). In addition, ETEC fimbriae are antigenically different. Thus, experimental vaccines developed from one specific fimbria could not provide protection against an ETEC strain expressing a different fimbria (42, 43). Moreover, recent evidence suggests that fimbriae may not function as protective antigens in the setting of naturally acquired infections and reinfections (7). Consequently, enterotoxin antigens have been reemphasized for ETEC vaccine development (43). Antitoxin vaccines currently under development largely use LT or its B subunit antigens because they are strongly immunogenic. The ST antigen cannot be used directly as a vaccine component because of its poor immunogenicity, unless it is coupled to a carrier protein and presented as a fusion or a chimeric protein (13, 22, 31, 38). Although a recent study suggested that anti-LT immunity may provide broader protection (14), experimental vaccine studies indicated that the induced anti-LT immunity provided protection only against LT-producing ETEC strains and not against ETEC strains that produce STa toxin (12, 13). As over two-thirds of human ETEC diarrhea cases and more than one-quarter of porcine ETEC diarrhea cases are caused by STa-producing ETEC strains (15, 16, 29, 30, 36, 45, 50), STa antigens must be included for developing broadly effective vaccines against ETEC infection.Porcine STa (pSTa), a protein that consists of 18 amino acids (human STa [hSTa] consists of 19 amino acids), is poorly immunogenic (35, 41). To include pSTa as a vaccine component, we need to enhance pSTa immunogenicity. In addition, a native pSTa is not suitable to be used in developing safe vaccines because it is sufficiently toxic to cause diarrhea. Therefore, we need to attenuate the pSTa toxicity. It has been reported that shorter synthetic hSTa peptides or hSTa with disulfide bonds disrupted showed toxicity reduction (4, 5, 19, 40, 46, 47). Moreover, several shorter synthetic hSTa peptides that had the 12th, 13th, or 14th amino acid residue replaced showed a great reduction in toxicity (46, 47). However, these shorter synthetic or disulfide bond-disrupted hSTa peptides either had not been characterized for immunogenicity or failed to induce protective immunity. Only when a shorter hSTa or an hSTa mutant (with disulfide bonds disrupted) was genetically fused to a carrier protein, such as the B subunit of cholera toxin (CT) or hLT, did the hSTa antigen become immunogenic (9, 31, 32, 33). However, anti-STa immunity from these fusion antigens was not sufficiently characterized, and retention of STa toxicity in these fusion proteins could cause safety concerns for their application in vaccine development (7, 9).No studies have been conducted to enhance pSTa immunogenicity and its potential application in vaccines against porcine ETEC infections. In this study, we mutated the porcine estA gene at nucleotides encoding the 11th, 12th, and 13th amino acids (which are homologous to the 12th, 13th, and 14th amino acids of hSTa) for three pSTa toxoids. These pSTa toxoids, which had all disulfide bonds retained, showed a great reduction in toxicity when examined in vitro (by cyclic GMP [cGMP] enzyme-linked immunosorbent assay [ELISA]) and in vivo (by porcine gut loop assay and challenge studies in a piglet model). We then genetically fused the mutated full-length porcine eltAB and estA genes for pLT₁₉₂:pSTa-toxoid fusion proteins. Purified toxoid fusion antigens were used to immunize adult rabbits to assess anti-LT and anti-STa antigenicity and antibody neutralization and to immunize a pregnant sow to preliminarily evaluate anti-STa immunity in protection against infection from an STa-producing ETEC strain.     

Development of a DNA Microarray for Detection and Serotyping of Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a common pathogen worldwide causing infectious diarrhea, especially traveler''s diarrhea. Traditional physiological assays, immunoassays, and PCR-based methods for the detection of ETEC target the heat-labile enterotoxin and/or the heat-stable enterotoxin. Separate serotyping methods using antisera are required to determine the ETEC serogroup. In this study, we developed a DNA microarray that can simultaneously detect enterotoxin genes and the 19 most common O serogroup genes in ETEC strains. The specificity and reproducibility of this approach were verified by hybridization to 223 strains: 50 target reference or clinical strains and 173 other strains, including those belonging to other E. coli O serogroups and closely related species. The sensitivity of detection was determined to be 50 ng of genomic DNA or 10⁸ CFU per ml of organisms in pure culture. The random PCR strategy used in this study with minimal bias provides an effective alternative to multiplex PCR for the detection of pathogens using DNA microarrays. The assay holds promise for applications in the clinical diagnosis and epidemiological surveillance of pathogenic microorganisms.Enterotoxigenic Escherichia coli (ETEC) is the leading bacterial cause of infectious diarrhea in the developing world, causing infantile or cholera-like disease in all age groups (2). It is among the major etiologic agents, leading to an estimated 1.5 million deaths per year worldwide (13, 14). ETEC is also a major cause of traveler''s diarrhea (3, 8, 11) and the most common pathogen among the six recognized diarrheagenic categories of E. coli, especially in the developing world (18). ETEC strains produce one or both of the following two enterotoxins: heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST). Two classes of STs—STa and STb—and two variants of STa—STp (initially discovered in isolates from pigs) and STh (initially discovered in isolates from humans)—have been described. The elt, estA, and estB genes encode the enterotoxins LT, STa, and STb, respectively (6, 23, 26).The O antigen comprises the outermost domain of the lipopolysaccharide molecule and is attached to the core oligosaccharide on the surfaces of Gram-negative bacteria (20). O antigens are among the most variable cellular constituents, imparting antigenic specificity. The composition of the O chain differs from strain to strain; more than 180 O-antigen structures are produced by different E. coli strains (25). The most common O serogroups reported in ETEC are O6, O8, O11, O15, O25, O27, O78, O85, O114, O115, O126, O128, O139, O148, O149, O159, O166, O167, and O173 (5, 18, 19, 31).Detection of ETEC has long relied on detection of the enterotoxins LT and/or ST by physiological assays and immunoassays, and serotyping has depended on assays using O-serogroup-specific antisera. These traditional approaches are slow and labor-intensive, and assays using antisera can be impeded by cross-reactivity. PCR assays, which are more rapid, sensitive, and specific, have also been widely used for ETEC diagnosis (15, 24). However, molecular methods for the serotyping of ETEC have not been developed.Molecular detection and typing by PCR and microarray techniques have many advantages over traditional methods. DNA microarrays provide an efficient approach for the parallel detection and analysis of a large number of pathogenic microorganisms. This technique has been applied to the detection of pathogens from all kinds of biological samples, including water, food, and soil (4, 7, 12, 17, 21).In this study, we developed a DNA microarray for the detection and typing of ETEC. The genes encoding the enterotoxins LT and ST were used for the detection of ETEC, and the serogroup-specific genes wzx and/or wzy were used for the typing of the 19 most common ETEC O serogroups. The microarray was examined for its specificity and sensitivity, and the findings of this study indicate that it is highly sensitive and reproducible.     

Ancestral Lineages of Human Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a common cause of diarrhea among children living in and among travelers visiting developing countries. Human ETEC strains represent an epidemiologically and phenotypically diverse group of pathogens, and there is a need to identify natural groupings of these organisms that may help to explain this diversity. Here, we sought to identify most of the important human ETEC lineages that exist in the E. coli population, because strains that originate from the same lineage may also have inherited many of the same epidemiological and phenotypic traits. We performed multilocus sequence typing (MLST) on 1,019 ETEC isolates obtained from humans in different countries and analyzed the data against a backdrop of MLST data from 1,250 non-ETEC E. coli and eight ETEC isolates from pigs. A total of 42 different lineages were identified, 15 of which, representing 792 (78%) of the strains, were estimated to have emerged >900 years ago. Twenty of the lineages were represented in more than one country. There was evidence of extensive exchange of enterotoxin and colonization factor genes between different lineages. Human and porcine ETEC have probably emerged from the same ancestral ETEC lineage on at least three occasions. Our findings suggest that most ETEC strains circulating in the human population today originate from well-established, globally widespread ETEC lineages. Some of the more important lineages identified here may represent a smaller and more manageable target for the ongoing efforts to develop effective ETEC vaccines.Enterotoxigenic Escherichia coli (ETEC) infections are an important cause of childhood diarrhea and diarrheal deaths among young children in developing countries (59) and of diarrhea among travelers to these countries (6, 54). Human ETEC strains are E. coli that produce one or more of three plasmid-encoded protein enterotoxins called human heat-stable toxin (STh or STaII), porcine heat-stable toxin (STp or STaI), and heat-labile toxin (LT or LT-I). The enterotoxins induce secretion of salts and water into the intestinal lumen (29). Many ETEC strains also produce surface appendages, called colonization factors (CFs), which help anchor the bacteria to the small intestinal wall (20). The toxins and all but one known CF are plasmid encoded (20, 34).Human ETEC strains are phenotypically and epidemiologically diverse: more than 20 different CFs have thus far been described (20), the characterization of ETEC strains collected from different parts of the world has yielded 117 different serotypes (57), and some ETEC strains appear to be more pathogenic than others (9, 36, 46). This diversity poses a challenge for the ongoing efforts to develop effective ETEC vaccines (7). Many studies have shown that ETEC have emerged from E. coli on several occasions, probably through horizontal transfer of the enterotoxin-encoding virulence plasmids, and that some of these ETEC lineages appear to be widespread (4, 11, 31-33, 37, 38, 43, 47, 51). Because strains that originate from the same ETEC lineage may also have inherited many of the same epidemiological and phenotypic traits, identifying and defining these lineages may improve our understanding of the ETEC diversity and may lead to the identification of lineage-specific protective antigens that can be used in vaccines. To identify these lineages, we performed multilocus sequence typing (MLST) and phylogenetic analyses on a collection of ETEC strains that had been isolated from humans in different countries. We also estimated each lineage''s age as a measure of how stable and well established these lineages are in the E. coli population. If the ancestral origin of the human ETEC population changes frequently, it would complicate efforts to identify new, chromosomally encoded antigens capable of inducing protective immune responses against ETEC. In that case, today''s main vaccine development strategy of targeting plasmid-encoded virulence factors, such as the toxins and CFs, would probably continue to be the best approach for developing effective ETEC vaccines.     

Toxin-Mediated Effects on the Innate Mucosal Defenses: Implications for Enteric Vaccines

Recent studies have confirmed older observations that the enterotoxins enhance enteric bacterial colonization and pathogenicity. How and why this happens remains unknown at this time. It appears that toxins such as the heat-labile enterotoxin (LT) from Escherichia coli can help overcome the innate mucosal barrier as a key step in enteric pathogen survival. We review key observations relevant to the roles of LT and cholera toxin in protective immunity and the effects of these toxins on innate mucosal defenses. We suggest either that toxin-mediated fluid secretion mechanically disrupts the mucus layer or that toxins interfere with innate mucosal defenses by other means. Such a breach gives pathogens access to the enterocyte, leading to binding and pathogenicity by enterotoxigenic E. coli (ETEC) and other organisms. Given the common exposure to LT⁺ ETEC by humans visiting or residing in regions of endemicity, barrier disruption should frequently render the gut vulnerable to ETEC and other enteric infections. Conversely, toxin immunity would be expected to block this process by protecting the innate mucosal barrier. Years ago, Peltola et al. (Lancet 338:1285-1289, 1991) observed unexpectedly broad protective effects against LT⁺ ETEC and mixed infections when using a toxin-based enteric vaccine. If toxins truly exert barrier-disruptive effects as a key step in pathogenesis, then a return to classic toxin-based vaccine strategies for enteric disease is warranted and can be expected to have unexpectedly broad protective effects.Enterotoxigenic Escherichia coli (ETEC) infection and cholera are toxin-mediated enteric diseases that are leading causes of morbidity and mortality worldwide (25, 32, 36). Although cholera is generally less frequent than ETEC infection, both cholera and ETEC infection can result in severely dehydrating diarrheal disease (73). While there is a cholera vaccine that confers protection against cholera for up to 3 years (11), there is, by contrast, currently no licensed vaccine to protect humans against ETEC disease. The establishment of a vaccine against ETEC is a major unmet need for both travelers and children in the developing world, as ETEC disease creates an extensive disease burden in both children (94) and travelers (85) and ranks as a top global health priority.The pathogenesis of cholera and that of ETEC disease are quite similar. Each begins with the ingestion of inocula, followed by elaboration of toxin, bacterial colonization, induction of profuse watery diarrhea, and dissemination of organisms back into the environment. The many similarities between cholera and ETEC disease are striking (13, 84), especially in regard to the centrality of the toxins to their pathogenicity. Vibrio cholerae secretes cholera toxin (CT), whereas ETEC elaborates both the heat-labile enterotoxin LT and the heat stable toxin ST. Both LT and CT are 86 kDa A:B5 ADP-ribosylating exotoxins that are functionally and structurally homologous (ca. 80%), highly immunogenic, and characterized by high levels of cross-neutralizing immunity. From a vaccine development perspective, this high level of homology may allow cholera and LT-containing ETEC disease to be addressed simultaneously in a single vaccine (10). However, ETEC disease differs from cholera in that many strains also produce the diarrheagenic heat-stable toxin (ST), a small, poorly immunogenic peptide. The question that remains is whether toxin-based vaccine protection against ST⁺ ETEC strains can be achieved (12, 69). The presence of ST toxin-containing strains complicates ETEC vaccine development, especially given that in some geographic regions ST-containing strains appear to be predominant (36, 72). However, efficacy data from vaccine trials have suggested that LT toxin-neutralizing immunity protects against LT⁺ ETEC and to some degree against both ST⁺ ETEC and non-ETEC organisms (9, 10, 68), indicating that LT toxin immunity may have unexpectedly broad effects. The goals of this review are to consider the role of LT toxin in ETEC pathogenicity in the context of the innate mucosal defenses and to consider how LT immunity may be protective in this context, leading to vaccine protection against non-LT-containing organisms.The intact, innate gut defenses, a combination of mechanical, chemical, environmental, and innate and adaptive immune effectors, are generally sufficient to ward off microbial infections. Consequently, organisms causing enteric diseases have developed a series of strategies to penetrate, disrupt, or modify the innate mucosal barrier, rendering the gut wall susceptible to subsequent pathogen colonization or entry (65). CT and the heat-labile (LT) enterotoxins are exotoxins that have long been known to cause the secretory diarrhea characteristic of these diseases, but the survival advantage the microbe gains by producing these toxins is debated. It has long been suggested that CT aids efficient pathogen colonization in the intestine, and more recent studies have confirmed that LT toxins enhance enteric bacterial colonization and pathogenicity (1, 2, 15, 44). As enteric pathogens must overcome the innate mucosal barrier to cause disease, we suggest here that toxins such as LT and CT are specifically produced to overcome the innate mucosal barrier as a key step in enteric pathogen survival. Given the common exposure of humans visiting or residing in regions with CT-containing vibrios and LT-containing ETEC (see below), one would predict that toxin exposure and subsequent barrier disruption would frequently render the gut generally vulnerable to enteric infection as the toxin-mediated breach in the mucosa is exploited. The corollary is that elimination of localized toxin effects through antitoxin neutralizing immunity could be expected to interrupt a strategy central to the survival of ETEC and possibly other coinfecting enteric pathogens.     

Children with the Le(a+b?) Blood Group Have Increased Susceptibility to Diarrhea Caused by Enterotoxigenic Escherichia coli Expressing Colonization Factor I Group Fimbriae

Recent studies have shown that children with blood group A have increased susceptibility to enterotoxigenic Escherichia coli (ETEC) diarrhea and that Lewis blood group “a” antigen (Le^a) may be a candidate receptor for ETEC colonization factor (CF) antigen I (CFA/I) fimbriae. Based on these findings, we have attempted to determine if children with the Le(a+b−) phenotype may be more susceptible to diarrhea caused by ETEC, in particular ETEC expressing CFA/I and related fimbriae of the CFA/I group, than Le(a−b+) children. To test this hypothesis, we have determined the Lewis antigen expression in 179 Bangladeshi children from a prospective birth cohort study in urban Dhaka in which ETEC expressing major CFs such as CFA/I, CS3, CS5, and CS6 was the most commonly isolated diarrhea pathogen during the first 2 years of life. The Lewis blood group phenotypes were determined by a dot blot immunoassay using saliva samples and by a tube agglutination test using fresh red blood cells. The results indicate that Le(a+b−) children more often had symptomatic than asymptomatic ETEC infections (P < 0.001), whereas symptomatic and asymptomatic ETEC infections were equally frequent in Le(a−b+) children. We also show that children with the Le(a+b−) blood type had significantly higher incidences of diarrhea caused by ETEC expressing fimbriae of the CFA/I group than Le(a−b+) children (P < 0.001). In contrast, we did not find any association between the Lewis blood group phenotype and diarrhea caused by ETEC expressing CS6 or rotavirus.Expression of Lewis or ABO histo-blood group types has been shown to be associated with different risks of enteric infections (4, 5, 12, 15, 24, 27), presumably through differential expression of cell surface glycoconjugates that are used as receptors for pathogens of the intestinal mucosa. The Lewis blood group antigens on the intestinal mucosa are synthesized through a group of glycosyltransferases, which insert fucose residues in type 1 and type 2 oligosaccharide precursors (21, 29, 30). The synthesis of Lewis antigens is dependent on the FUT2 and FUT3 genes. If both genes are functional, the phenotype will be Le(a−b+), i.e., the secretor type, whereas individuals in whom the FUT2 gene is not expressed will have the Le(a+b−) phenotype, i.e., the nonsecretor type. Failure to express both FUT2 and FUT3 will result in Le(a−b−) (9).A predisposition for obtaining dehydrating cholera has been seen in blood group O individuals (8, 12, 14, 19, 28). In contrast, our recent study showed that enterotoxigenic Escherichia coli (ETEC) diarrheal episodes were more common in children with blood group AB or A than in individuals with blood group O (24). We have also shown that colonization factor (CF) antigen I (CFA/I) expressed by ETEC binds to glycosphingolipids that are associated with blood group antigens, e.g., Le^a, that may be expressed on epithelial cells in the small intestine in humans (16). The glycosphingolipid binding capacity of CFA/I fimbriae resides in the major CfaB subunit protein (3, 8, 16). CFA/I was the first identified human-specific CF of ETEC bacteria (11). Subsequently, seven other genetically related fimbriae, CS1, CS2, CS4, CS14, CS17, CS19, and putative CF O71, denoted as the CFA/I group (1), have been shown to be related to CFA/I both in the structural subunits (26) and tip-localized minor adhesive subunits (1). A glycosphingolipid binding pattern similar to that of CFA/I has been demonstrated for CS1 and CS4 that might be due to related N-terminal sequences (3, 8, 16). In addition, in another study (25) we have also shown that the conserved regions of the CF subunit proteins (shared by the CFA/I group fimbriae) are likely to be responsible for the receptor binding, since monoclonal antibodies against this region prevented enterocyte binding and protected against challenge with ETEC expressing CFA/I and CS4.In a recent longitudinal birth cohort (BC) study in Dhaka, we showed that ETEC was a major pathogen in children up to 2 years old and that a high proportion of symptomatic infections were caused by ETEC expressing the CFA/I group fimbriae (24). In this study, we present additional data to determine whether children with specific Lewis blood group antigen phenotypes, e.g., Le(a+b−) or Le(a−b+), have different susceptibilities to diarrhea caused by ETEC, in particular ETEC expressing the CFA/I group fimbriae, as well as susceptibilities to diarrhea caused by rotavirus.     

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.     

Testing the Efficacy and Toxicity of Adenylyl Cyclase Inhibitors against Enteric Pathogens Using In Vitro and In Vivo Models of Infection

Enterotoxigenic Escherichia coli (ETEC) produces the ADP-ribosyltransferase toxin known as heat-labile enterotoxin (LT). In addition to the toxic effect of LT resulting in increases of cyclic AMP (cAMP) and disturbance of cellular metabolic processes, this toxin promotes bacterial adherence to intestinal epithelial cells (A. M. Johnson, R. S. Kaushik, D. H. Francis, J. M. Fleckenstein, and P. R. Hardwidge, J. Bacteriol. 191:178-186, 2009). Therefore, we hypothesized that the identification of a compound that inhibits the activity of the toxin would have a suppressive effect on the ETEC colonization capabilities. Using in vivo and in vitro approaches, we present evidence demonstrating that a fluorenone-based compound, DC5, which inhibits the accumulation of cAMP in intoxicated cultured cells, significantly decreases the colonization abilities of adenylyl cyclase toxin-producing bacteria, such as ETEC. These findings established that DC5 is a potent inhibitor both of toxin-induced cAMP accumulation and of ETEC adherence to epithelial cells. Thus, DC5 may be a promising compound for treatment of diarrhea caused by ETEC and other adenylyl cyclase toxin-producing bacteria.Diarrheal diseases caused by enteric pathogens such as enterotoxigenic Escherichia coli (ETEC) or Vibrio cholerae remain a major cause of morbidity and mortality worldwide (25, 31, 34). ETEC, a pathogen of increasing frequency in the United States, is a leading cause of traveler''s diarrhea (36). Prevention of diarrhea caused by these toxigenic organisms, by virtue of improved hygiene and provision of sanitation and water treatment, often is impractical in most developing countries, where the morbidity and mortality rates are highest (37). ETEC and V. cholerae produce the heat-labile toxin (LT) and cholera toxin (CT), respectively, and both toxins display ADP ribosylation activity, which results in increased chloride and water efflux into the intestinal lumen, leading to significant volumes of watery diarrhea (25). Interestingly, recent studies have confirmed prior observations indicating that enterotoxins, such as LT and CT, enhance enteric bacterial colonization and pathogenicity (reviewed in reference 8). Anti-toxigenic compounds have been shown to decrease morbidity and mortality of diseases caused by other toxin-producing bacteria (18, 29). Therapy using anti-toxigenic compounds is therefore an area of great interest. Identification of a new class of drugs that afford selective anti-toxigenic activities would constitute a highly desired compound useful for future therapy; however, these drugs need to be experimentally validated by first testing efficacy, bioavailability, and the absence of toxicity in relevant animal models.We have previously shown that prostaglandin E₂-histidine (PGE₂-l-histidine) and prostaglandin E₂-imidazole (PGE₂-imidazole) adducts significantly reduced CT-induced fluid loss and cyclic AMP (cAMP) accumulation in the murine ligated small intestinal loop model (21). These and other derived adducts have been shown to act on ETEC LT and on the edema factor (EF) produced by Bacillus anthracis (15). Our recent progress has resulted in the development of structurally stable compounds that inhibit toxin-induced accumulation of cAMP in in vitro cell culture assays (3). Our studies have shown that although some of these compounds are extremely active in vitro and showed reduced fluid accumulation in the murine model of experimental cholera, they were also toxic, causing destruction and bleeding of the intestinal lumen (unpublished data). Further, we have also identified nontoxic compounds that inhibited fluid accumulation caused by CT injection in a murine intestinal loop model (unpublished data). The mouse intestinal loop assay, however, is somewhat artificial because the intestine remains ligated, preventing normal flow of the intestinal contents, which is important in testing the efficacy of the compound. Because one of our goals is to identify a compound(s) that can protect against diarrhea caused by a whole organism in a natural setting and not just by purified toxins, in the current study, we utilized a murine model that mimics more closely the infection route used by ETEC (2, 6, 21, 24, 28). We hypothesized that the murine model of experimental diarrhea using ETEC bacteria not only was an appropriate way to distinguish between those compounds that are effective against the toxin but might also help to identify possible toxic effects in vivo. This method provided the advantage of being minimally invasive; the flow in the intestine was not interrupted, and the method provided the advantage of being able to determine that the organism was capable of colonizing the small-intestine mucosa while being affected by the tested compound. Using this method, we established evidence demonstrating that a novel toxin inhibitor, 3-[(9-oxo-9H-fluorene-1-carbonyl)-amino]-benzoic acid, called DC5 (3, 4), which inhibits the accumulation of cAMP in cultured cells, significantly decreased the fluid loss caused by the LT and reduced the colonization activity of ETEC strains.     

Characteristics of Meropenem Heteroresistance in Klebsiella pneumoniae Carbapenemase (KPC)-Producing Clinical Isolates of K. pneumoniae

Meropenem heteroresistance was investigated in six apparently meropenem-susceptible, Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) clinical isolates, compared with that in carbapenemase-negative, meropenem-susceptible controls. In population analyses, the KPC-KP isolates grew at meropenem concentrations of 64 to 256 μg/ml. Heteroresistant colonies had significantly elevated expression of the bla_KPC gene compared with the native populations but did not retain heteroresistance when subcultured in drug-free media. Time-kill assays indicated that meropenem alone was not bactericidal against KPC-KP but efficiently killed the control strains.Since the beginning of the last decade, Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) isolates have been increasingly detected in the United States and subsequently in several regions worldwide (3, 4, 13, 17, 21). KPC enzymes efficiently hydrolyze all β-lactam molecules (1, 22), conferring various levels of resistance to all β-lactam compounds, including carbapenems (13). However, KPC-producing K. pneumoniae may appear susceptible to carbapenems, mainly meropenem (2, 13), by reference CLSI agar dilution or broth microdilution methods as well as by automated systems (6, 15, 17). Characteristically, it has been reported that automated systems may identify as many as 87% of KPC-KP isolates to be susceptible to meropenem (13). The detection of the susceptibility level of KPC-KP isolates to carbapenems has been shown to be difficult due to the phenotypic heterogeneity that they commonly exhibit (3, 10, 13). For instance, in agar diffusion methods such as disk diffusion or Etest, the heterogeneous growth to carbapenems of KPC-KP results in the appearance of scattered colonies within the inhibition zones (9, 13).These issues raise the need for cautious evaluation of susceptibility testing in KPC-KP isolates that are recovered in clinical laboratories. In our clinical laboratories, several KPC-KP isolates that appear susceptible by automated susceptibility assays or reference dilution assays contain heterogeneous subpopulations (D. Sofianou and K. Themeli-Digalaki, personal communications). It has been also shown that among Greek KPC-KP isolates, meropenem tends to exhibit lower MICs than imipenem or ertapenem (17, 20). In that respect, the aim of the present study was to characterize the heterogeneous mode of growth of apparently meropenem-susceptible KPC-KP clinical isolates by population analyses and bactericidal assays.     

Lipoprotein Lipase and Hydrofluoric Acid Deactivate Both Bacterial Lipoproteins and Lipoteichoic Acids,but Platelet-Activating Factor-Acetylhydrolase Degrades Only Lipoteichoic Acids

To identify the Toll-like receptor 2 ligand critically involved in infections with gram-positive bacteria, lipoprotein lipase (LPL) or hydrogen peroxide (H₂O₂) is often used to selectively inactivate lipoproteins, and hydrofluoric acid (HF) or platelet-activating factor-acetylhydrolase (PAF-AH) is used to selectively inactivate lipoteichoic acid (LTA). However, the specificities of these chemical reactions are unknown. We investigated the reaction specificities by using two synthetic lipoproteins (Pam₃CSK₄ and FSL-1) and LTAs from pneumococci and staphylococci. Changes in the structures of the two synthetic proteins and the LTAs were monitored by mass spectrometry, and biological activity changes were evaluated by measuring tumor necrosis factor alpha production by mouse macrophage cells (RAW 264.7) following stimulation. PAF-AH inactivated LTA without reducing the biological activities of Pam₃CSK₄ and FSL-1. Mass spectroscopy confirmed that PAF-AH monodeacylated pneumococcal LTA but did not alter the structure of either Pam₃CSK₄ or FSL-1. As expected, HF treatment reduced the biological activity of LTA by more than 80% and degraded LTA. HF treatment not only deacylated Pam₃CSK₄ and FSL-1 but also reduced the activities of the lipoproteins by more than 60%. Treatment with LPL decreased the biological activities by more than 80%. LPL also removed an acyl chain from the LTA and reduced its activity. Our results indicate that treatment with 1% H₂O₂ for 6 h at 37°C inactivates Pam₃CSK₄, FSL-1, and LTA by more than 80%. Although HF, LPL, and H₂O₂ treatments degrade and inactivate both lipopeptides and LTA, PAF-AH selectively inactivated LTA with no effect on the biological and structural properties of the two lipopeptides. Also, the ability of PAF-AH to reduce the inflammatory activities of cell wall extracts from gram-positive bacteria suggests LTA to be essential in inflammatory responses to gram-positive bacteria.Bacterial sepsis is a leading cause of death within intensive care units (43). Although bacterial sepsis was traditionally associated with gram-negative (Gr−) bacteria, recently, the prevalence of sepsis caused by gram-positive (Gr+) bacteria has rapidly increased (2, 3, 38). In fact, in 2000, Gr+ bacteria accounted for 52% of sepsis cases whereas Gr− bacteria accounted for only 37.6% (7, 31, 38). In bacterial sepsis, the innate immune system provides both the initial immune responses and the early inflammatory responses (1, 8, 12). Early responses to infections with Gr+ and Gr− bacteria have been shown in previous studies to involve different cytokine profiles (9, 16, 25, 51, 54). Other studies have found that infections with Gr− bacteria activate Toll-like receptor 4 (TLR4) primarily with lipopolysaccharide (LPS), a membrane component of Gr− bacteria (26, 27, 44, 53). In contrast, infections with Gr+ bacteria involve TLR2, but the nature of the key TLR2 ligand is still controversial (34, 52, 56).Two components of the cell walls of Gr+ bacteria have been proposed to be TLR2 ligands. One group of studies suggests that lipoteichoic acid (LTA) is the key ligand (10, 46, 49, 57). LTA is a polyphosphate attached to the cell membrane via a diacyl glycolipid and is an abundant component of the envelopes of Gr+ bacteria (47). Highly purified LTA, as well as its synthetic analogs, has been shown to trigger TLR2-mediated inflammatory responses (10, 15, 20, 35). However, the biological role of the LTA is unclear because it is difficult to purify natural LTA without introducing contaminants or damaging the structure of the LTA (41). Another group proposes bacterial lipoproteins as the critical ligand (22). Lipoproteins are a functionally diverse class of bacterial membrane proteins characterized by an N-terminal lipid moiety (4) and are TLR2 ligands (22-24). Although synthetic analogs of lipoproteins were found to be potent TLR2 ligands (5, 6, 42), natural lipoproteins are difficult to purify, and their properties are poorly understood.To avoid the technical difficulties involved in purification, a different investigational approach was developed. This approach uses methods to selectively inactivate either LTA or lipoproteins in bacterial culture supernatants or crude bacterial cell wall extracts (22-24, 49). LTA inactivation is usually performed with hydrofluoric acid (HF) or platelet-activating factor-acetylhydrolase (PAF-AH) (23, 48, 49), which, respectively, hydrolyzes the phosphodiester bonds in the LTA or deacylates one of its acyl chains (17, 28, 36, 55). Lipoprotein inactivation is commonly achieved by deacylation with a lipoprotein lipase (LPL) or by oxidation with hydrogen peroxide (H₂O₂) (22, 24, 62). Despite their wide use, the reaction selectivities of these methods have not been evaluated. Thus, we investigated the reaction specificities of these methods by studying the impacts of these four reactions on the biological properties as well as the chemical structures of LTA and lipoprotein analogs.     

Shiga Toxin 2 Targets the Murine Renal Collecting Duct Epithelium

Hemolytic-uremic syndrome (HUS) caused by Shiga toxin-producing Escherichia coli infection is a leading cause of pediatric acute renal failure. Bacterial toxins produced in the gut enter the circulation and cause a systemic toxemia and targeted cell damage. It had been previously shown that injection of Shiga toxin 2 (Stx2) and lipopolysaccharide (LPS) caused signs and symptoms of HUS in mice, but the mechanism leading to renal failure remained uncharacterized. The current study elucidated that murine cells of the glomerular filtration barrier were unresponsive to Stx2 because they lacked the receptor glycosphingolipid globotriaosylceramide (Gb₃) in vitro and in vivo. In contrast to the analogous human cells, Stx2 did not alter inflammatory kinase activity, cytokine release, or cell viability of the murine glomerular cells. However, murine renal cortical and medullary tubular cells expressed Gb₃ and responded to Stx2 by undergoing apoptosis. Stx2-induced loss of functioning collecting ducts in vivo caused production of increased dilute urine, resulted in dehydration, and contributed to renal failure. Stx2-mediated renal dysfunction was ameliorated by administration of the nonselective caspase inhibitor Q-VD-OPH in vivo. Stx2 therefore targets the murine collecting duct, and this Stx2-induced injury can be blocked by inhibitors of apoptosis in vivo.Shiga toxin-producing Escherichia coli (STEC) is the principal etiologic agent of diarrhea-associated hemolytic-uremic syndrome (HUS) (42, 60, 66). Renal disease is thought to be due to the combined action of Shiga toxins (Shiga toxin 1 [Stx1] and Stx2), the primary virulence factors of STEC, and bacterial lipopolysaccharide (LPS) on the renal glomeruli and tubules (6, 42, 60, 66). Of these, Stx2 is most frequently associated with the development of HUS (45). Shiga toxin enters susceptible cell types after binding to the cell surface receptor glycosphingolipid globotriaosylceramide (Gb₃) and specifically depurinates the 28S rRNA, thereby inhibiting protein synthesis (42, 60, 66). The damage initiates a ribotoxic stress response consisting of mitogen-activated protein (MAP) kinase activation, and this response can be associated with cytokine release and cell death (21, 22, 25-27, 61, 69, 73). This cell death is often caspase-dependent apoptosis (18, 61). Gb₃ is expressed by human glomerular endothelial cells, podocytes, and multiple tubular epithelial cell types, and damage markers for these cells can be detected in urine samples from HUS patients (10-12, 15, 49, 73). Shiga toxin binds to these cells in renal sections from HUS patients, and along with the typical fibrin-rich glomerular microangiopathy, biopsy sections demonstrate apoptosis of both glomerular and tubular cell types (9, 29, 31).Concomitant development of the most prominent features of HUS: anemia, thrombocytopenia, and renal failure, requires both Shiga toxin and LPS in the murine model (30, 33). Nevertheless, our previous work demonstrated that renal failure is mediated exclusively by Stx2 (33). While it is established that Gb₃ is the unique Shiga toxin receptor (46), the current literature regarding the mechanism by which Shiga toxin causes renal dysfunction in mice is inconsistent. Even though Gb₃ has been localized to some murine renal tubules and tubular damage has been observed (19, 23, 46, 53, 65, 68, 72, 74), the specific types of tubules affected have been incompletely characterized. Although multiple groups have been unable to locate the Shiga toxin receptor Gb₃ in glomeruli in murine renal sections (19, 53), one group has reported that murine glomerular podocytes possess Gb₃ and respond to Stx2 in vitro (40), and another group has reported that renal tubular capillaries express the Gb₃ receptor (46). Furthermore, murine glomerular abnormalities, including platelet and fibrin deposition, occur in some murine HUS models (28, 30, 33, 46, 59, 63). We demonstrate here that murine glomerular endothelial cells and podocytes are unresponsive to Stx2 because they do not produce the glycosphingolipid receptor Gb₃ in vitro or in vivo. Further, murine renal tubules, including collecting ducts, express Gb₃ and undergo Stx2-induced apoptosis, resulting in dysfunctional urine production and dehydration.     

Characterization and Studies of the Cellular Interaction of Native Colonization Factor CS6 Purified from a Clinical Isolate of Enterotoxigenic Escherichia coli

CS6 is a widely expressed colonization factor of enterotoxigenic Escherichia coli (ETEC). To date, CS6 has not been well characterized in its native state. Here, we purified CS6 for the first time from an ETEC clinical isolate. Purified CS6 was composed of two structural subunits, CssA and CssB, which were present in equal amounts and tightly linked through noncovalent, detergent-stable association. The CssA subunit was poorly immunogenic, whereas CssB was highly immunogenic. Although the predicted molecular mass of CssA is 15 kDa, the purified CssA has an effective molecular mass of 18.5 kDa due to fatty acid modification. When purified CS6 was screened for its ability to bind with different extracellular matrix proteins, fibronectin (Fn) was found to interact with CS6 as well as CssA in a dose-dependent and saturable manner. This interaction was inhibited both by a synthetic peptide corresponding to the C-terminal hydrophilic, surface-exposed region of CssA (positions 112 to 126) and by the antibody derived against this region. Enzyme-linked immunosorbent assay results showed that CssA interacted with the 70-kDa N-terminal domain of Fn. The modifications on CssA probably do not play a role in Fn binding. Preincubation of INT 407 cells with CssA, but not CssB, inhibited ETEC binding to these cells. The results suggested that CS6-expressing ETEC binds to Fn of INT 407 cells through the C-terminal region of CssA. Purified CS6 was found to colocalize with Fn along the junctions of INT 407 cells. Based on the results obtained, we propose that CS6-expressing ETEC binds to the intestinal cells through Fn for colonization.Enterotoxigenic Escherichia coli (ETEC) infection is the leading cause of infantile diarrhea in developing countries and an important etiologic agent for traveler''s diarrhea. ETEC accounts for approximately 210 million diarrhea episodes and 380,000 deaths annually (35). Community-based studies conducted in developing countries with children younger than 5 years have shown that ETEC was the most frequently isolated enteropathogen (34, 35). As a cause of traveler''s diarrhea, ETEC was found to be associated with 40 to 70% of the cases, with drastic outcome in terms of morbidity and economic consequences (34).In order to initiate pathogenesis, ETEC strains must adhere to the small intestine (14). This event is mediated by several proteinaceous surface antigens, collectively known as colonization factor antigens (CFAs) (6). To date, more than 25 distinct colonization factors have been identified, of which CS6 is the most prevalent in many countries (7, 20, 22). Many of the colonization factors have morphology of fimbriae or pili (14). However, the morphology of CS6 has not so far been defined. CS6 was assumed to be either a nonfimbrial or a short oligomeric assembly that does not protrude enough to be visualized under an electron microscope (17). Functional CS6 is expressed and transported to the bacterial surface in a chaperone-usher pathway. CssC and CssD are the chaperone and usher proteins, respectively, that help surface expression of the CS6 structural subunits, CssA and CssB (33).The role of CS6 in intestinal adherence has been demonstrated using CS6-expressing whole bacteria, but the receptor specificity is still unknown (11). A recent report has shown that when CssB is mutated, binding of bacteria to a colonic cell line (CaCo-2) is reduced slightly compared to that of the bacteria expressing whole CS6 (30).Here, we have purified CS6 to homogeneity from a clinical isolate of ETEC and separated its subunits (CssA and CssB) for the first time. We have characterized CS6 in its native form and demonstrated that fibronectin (Fn) is the interacting matrix for adherence. The carboxy-terminal (C-terminal) region of CssA plays a key role in this interaction with the amino-terminal (N-terminal) region of Fn.     

Involvement of quorum sensing and heat-stable enterotoxin a in cell damage caused by a porcine enterotoxigenic Escherichia coli strain

Enterotoxigenic Escherichia coli (ETEC) strains with K88 fimbriae are often associated with the outbreaks of diarrhea in newborn and weaned piglets worldwide. In the present study, we observed that 10⁸ CFU/ml of K88⁺ ETEC strain JG280 caused more death of pig intestinal IPEC-J2 cells than did 10⁹ CFU/ml, suggesting that ETEC-induced cell death was cell density dependent and that quorum sensing (QS) may play a role in pathogenesis. Subsequent investigations demonstrated a positive correlation between autoinducer 2 (AI-2) activity of JG280 and death of IPEC-J2 cells during the infection for up to 3 h. However, there was a negative correlation between AI-2 activity and expression of the JG280 enterotoxin genes estA and estB when IPEC-J2 cells were exposed to the pathogen at 10⁸ CFU/ml. We therefore cloned the luxS gene (responsible for AI-2 production) from JG280 and overexpressed it in E. coli DH5α, because deletion of the luxS gene was retarded by the lack of suitable antibiotic selection markers and the resistance of this pathogen to a wide range of antibiotics. The addition of culture fluid from E. coli DH5α with the overexpressed luxS reduced cell death of IPEC-J2 cells by 10⁸ CFU/ml JG280. The addition also reduced the estA expression by JG280. Nonpathogenic K88⁺ strain JFF4, which lacks the enterotoxin genes, caused no death of IPEC-J2 cells, although it produced AI-2 activity comparable to that produced by JG280. These results suggest the involvement of AI-2-mediated quorum sensing in K88⁺ ETEC pathogenesis, possibly through a negative regulation of STa production.Enterotoxigenic Escherichia coli (ETEC) is an important pathogen causing severe watery diarrhea in farm animals, especially postweaning diarrhea in pigs (12). In humans, ETEC is the most common cause of traveler''s diarrhea and can be fatal for children under 5 years of age (6, 9, 16). ETEC strains are characterized by the production of adhesins that mediate bacterial adherence to the intestine and enterotoxins that elicit diarrhea. The most common and severe infections in pigs are caused by ETEC strains carrying F4 (K88) and F18 fimbrial adhesins (21). After binding of the fimbriae to enterocytes, ETEC strains proliferate rapidly to attain massive numbers and produce one or more types of enterotoxin, including heat-stable enterotoxins (STs) and heat-labile enterotoxin (LT) (22), which stimulate fluid and electrolyte secretion by intestinal cells, thus leading to diarrhea. Other virulence factors, including SepA (sepA), which belongs to a family of proteins from enteropathogenic (32) and enterohemorrhagic (7) E. coli, and Paa (paa), porcine attaching-effacing-associated protein (5), may also contribute to ETEC pathogenesis.Previous in vitro studies with pig intestinal epithelial (IPEC-J2) cells showed that infection with a wild-type (wt) ETEC strain (expressing LT and STb toxins) (3) significantly increased cell death and phosphatidylserine (PS) exposure on the outer leaflet of IPEC-J2 cells (14). In addition, infection with both the ΔeltAB (an isogenic mutant deficient in LT expression) and ΔeltAB/pLT (ΔeltAB mutant complemented by plasmid-based eltAB expression) ETEC strains also modestly increased death of IPEC-J2 cells (14). Another ETEC strain, B41M, that expresses STa toxin was also reported to induce IPEC-J2 cell damage (14). Previous in vivo studies also showed that enterotoxins LT and STb secreted by ETEC contributed significantly to the severity of diarrhea in gnotobiotic piglets, and deletion of estB and eltAB could prevent the development of electrolyte imbalances and dehydration of piglets (11). However, it is still unclear how much each of the enterotoxins contributes to ETEC pathogenesis.Diarrheagenic E. coli strains regulate their virulence gene expression in response to a variety of environmental factors and use quorum sensing (QS) to respond to their cell population to coordinate virulence gene expression (10). QS is a bacterial cell-to-cell communication mechanism, involving the production and detection of autoinducers (AIs). QS may be involved in the regulation of virulence factors, including the type III secretion system in enterohemorrhagic E. coli (EHEC) and enteropathogenic E. coli (EPEC) (29). A breakthrough discovery of a new signaling molecule, AI-3, whose synthesis is not dependent on LuxS (35), indicates that this molecule may be involved in EHEC cross talk with the epinephrine-norepinephrine host signaling system (30). QseBC (a two-component system) was reported to be activated by QS through the AI-3 system (31) and is responsible for the regulation of flagella and motility (31).To our knowledge, the role of QS in ETEC pathogenesis has not been reported. In the present study, we observed that K88⁺ ETEC strain-induced damage of cultured pig intestinal epithelial cells was bacterial cell density dependent, which suggests the involvement of QS. Further studies were carried out to determine possible roles of AI-2 of K88⁺ ETEC in causing the cell damage and regulating the expression of enterotoxin genes.     

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.     

Molecular Identification and Susceptibility of Trichosporon Species Isolated from Clinical Specimens in Qatar: Isolation of Trichosporon dohaense Taj-Aldeen,Meis & Boekhout sp. nov.

Trichosporon species have been reported as emerging pathogens and usually occur in severely immunocompromised patients. In the present work, 27 clinical isolates of Trichosporon species were recovered from 27 patients. The patients were not immunocompromised, except for one with acute myeloid leukemia. Sequence analysis revealed the isolation of Trichosporon dohaense Taj-Aldeen, Meis & Boekhout sp. nov., with CBS 10761^T as the holotype strain, belonging to the Ovoides clade. In the D1-D2 large-subunit rRNA gene analysis, T. dohaense is a sister species to T. coremiiforme, and in the internal transcribed spacer analysis, the species is basal to the other species of this clade. Molecular identification of the strains yielded 17 T. asahii, 3 T. inkin, 2 T. japonicum, 2 T. faecale, and 3 T. dohaense isolates. The former four species exhibited low MICs for five antifungal azoles but showed high MICs for amphotericin B. T. dohaense demonstrated the lowest amphotericin B MIC (1 mg/liter). For the majority of T. asahii isolates, amphotericin B MICs were high (MIC at which 90% of isolates were inhibited [MIC₉₀], ≥16 mg/liter), and except for fluconazole (MIC₉₀, 8 mg/liter), the azole MICs were low: MIC₉₀s were 0.5 mg/liter for itraconazole, 0.25 mg/liter for voriconazole, 0.25 mg/liter for posaconazole, and 0.125 mg/liter for isavuconazole. The echinocandins, caspofungin and anidulafungin, demonstrated no activity against Trichosporon species.Trichosporon species are yeast-like fungi, widely distributed in nature and commonly isolated from soil and other environmental sources, which have been involved in a variety of opportunistic infections and have been recognized as emerging fungal pathogens in immunocompromised hosts (19, 79, 80). Disseminated Trichosporon infections are potentially life-threatening and are often fatal in neutropenic patients (7, 22). Although uncommon, pathogenic species of this genus have been reported increasingly, mostly in patients with malignant diseases (3, 6, 9, 10, 11, 20, 32, 44, 47, 48, 63, 77), neonates (18, 56, 84), a bone marrow transplant recipient (22), a solid organ transplant recipient (50), and patients with human immunodeficiency virus (34, 35, 46). Trichosporon has also been reported to cause fungemia (5, 9, 25, 29, 30, 33, 53, 62). Members of the genus Trichosporon have occasionally been implicated as nail pathogens (16, 28, 74) and in subcutaneous infections (66). Trichosporon is considered an opportunistic agent, and therefore, recovery of Trichosporon species capable of growing at 37°C, especially from immunocompromised patients, should be regarded as potentially significant. Several reports have addressed the difficulty of identifying Trichosporon to the species level by physiological and biochemical characteristics (2, 64); therefore, molecular methods based on the sequencing of the internal transcribed spacer (ITS) have been developed (15, 69, 71, 72).In the present paper, we report the isolation of Trichosporon species from clinical specimens over a 4-year period in Qatar, the poor performance of biochemical identification methods, the significance of molecular identification, and the antifungal susceptibility data for the isolates. While investigating the molecular identification of Trichosporon species, we found three strains that do not match any of the published strains in the literature. We describe this organism as Trichosporon dohaense Taj-Aldeen, Meis & Boekhout, sp. nov., the name proposed for this species.     

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.