K-1 Antigen Content and the Presence of an Additional Sialic Acid-Containing Antigen Among Bacteremic K-1 Escherichia coli: Correlation with Susceptibility to Opsonophagocytosis

Eighty percent of blood culture isolates of Escherichia coli K-1 are resistant to in vitro opsonophagocytosis by normal human granulocytes and fresh serum. To determine the basis for susceptibility to phagocytosis in 20% of bacteremic K-1 E. coli, we investigated possible quantitative and qualitative immunochemical differences in the K-1 antigen content among resistant and sensitive isolates. We prepared extracts of blood culture K-1 E. coli by sonication and determined the K-1 polysaccharide content per dry weight of bacteria by rocket immunoelectrophoresis using cross-reactive equine anti-group B meningococcal sera. We assessed qualitative differences in the antigen content by crossed immunoelectrophoresis, using an immune globulin fraction and isolated immunoglobulin G (IgG) and IgM from the group B antisera. Three different resistant K-1 isolates contained a mean K-1 content of 48.5 ± 7.6 μg/mg ± standard deviation of dry bacteria, and three sensitive isolates contained 23.2 ± 5.6 μg/mg (P < 0.005). Crossed immunoelectrophoresis of extracts from both sensitive and resistant strains revealed a secondary sialic acid-containing antigen that was electrophoretically different from both the major K-1 antigen and a reference group B meningococcal antigen. This negatively charged secondary antigen was susceptible to Clostridium perfringens neuraminidase degradation and reacted only with IgG whereas the major K-1 antigen reacted only with IgM. This antigen was detected in the extracts of resistant isolates only at 10¹⁰ but not at 10⁹ colony-forming units per milliliter. This study demonstrates that (i) the degree of phagocytosis of bacteremic E. coli K-1 isolates is inversely associated with K-1 content, and (ii) more easily phagocytosed (sensitive) K-1 isolates have greater amounts of an additional sialic acid-containing antigen that appears to be unrelated to the previously described O acetyl K-1 antigen.     

Evidence of Pathogenic Subgroups among Atypical Enteropathogenic Escherichia coli Strains

We describe the characterization of 126 atypical enteropathogenic Escherichia coli (aEPEC) isolates from 1,749 Brazilian children. Classic aEPEC strains were more frequently found in children with diarrhea than in controls (P < 0.001), showing their importance as acute diarrhea agents in our country. Only aEPEC strains carrying either the ehxA or paa gene were significantly associated with diarrhea.Enteropathogenic Escherichia coli (EPEC), one of the six E. coli diarrheagenic pathotypes, produces an adherence factor chromosomally encoded by the eae (EPEC attaching and effacing) gene located within the locus for enterocyte effacement (LEE) pathogenicity island (15, 16, 18).“Typical” EPEC strains contain, in addition to eae, the EPEC adherence factor (EAF) plasmid (4), which encodes the bundle-forming pili that mediate localized adherence to epithelial cells (9, 26). EPEC strains lacking the EAF plasmid have been designated “atypical” EPEC (aEPEC) (12). Whereas typical EPEC strains express only the virulence factors encoded by the LEE region and the EAF plasmid, aEPEC strains have additional virulence properties (11, 32).Recently Afset et al. (2) described several virulence genes associated with diarrhea in aEPEC isolates from Norwegian children. In their study, genes belonging to the pathogenicity island OI-122 (efa1/lifA, nleB, nleE, and sen), present in the enterohemorrhagic E. coli (EHEC) reference strain EDL933 (17), and the gene for long polar fimbriae (lpfA) (10), found in EHEC O113 strains, were particularly frequent. Other genes, such as the porcine A/E-associated gene (paa) (5) and the EHEC hemolysin gene (ehxA) (27), were also found to be associated with diarrheal disease.Other E. coli adhesion factors recently described include the protein ToxB, required for full adherence expression in EHEC O157:H7 (30); Iha, an adherence-conferring protein similar to Vibrio cholerae IrgA (29); Saa, an autoagglutinating adhesin identified in LEE-negative strains (22); and Spf, a sorbitol-fermenting EHEC O157 fimbria (8). In addition, we recently identified a diffuse adherence (lda) locus in an aEPEC strain of the O26 serogroup that codes for adherence to HEp-2 cells (25).In this report, we describe the prevalence and virulence profile of aEPEC strains isolated from diarrhea patients and control subjects in several cities of Brazil from 1999 through 2004.Stool specimens from 1,102 children under 2 years of age with diarrhea, presenting to the emergency room of public hospitals in seven cities representing different regions of Brazil, and 647 randomly selected children without any gastrointestinal symptoms from the same hospitals were studied. All specimens were investigated for the presence of enteric pathogens, such as diarrheagenic E. coli, Shigella species, Salmonella species, Yersinia enterocolitica, Campylobacter species, and rotavirus (24).Atypical EPEC strains were isolated, identified, and serotyped as described elsewhere (11). One isolate per subject was stored at −70°C.aEPEC strains were screened by colony blot hybridization with 16 different DNA probes representing a panel of toxin, adhesin, and OI-122 genes. Fourteen DNA probes were prepared by PCR amplification from prototype strains. The genes, primers, amplicon size, PCR conditions, and prototype strains are given in Table ​Table1.1. Two DNA probes were prepared by plasmid extraction using the method of Birnboim and Doly (7) and digestion with appropriate restriction endonucleases. The cdt probe was a 1,357-bp fragment from plasmid pCVD448 (28), and the cnf probe was a 335-bp fragment of pEOSW1 (20). The probes were then purified by gel extraction (23) and labeled with [α-³²P]dCTP, and colony hybridization assays were performed as described elsewhere (24).

TABLE 1.

PCR primers and conditions used in this study and sizes of PCR amplicons

Similarity and Divergence among Adherent-Invasive Escherichia coli and Extraintestinal Pathogenic E. coli Strains

Adherent-invasive Escherichia coli (AIEC) pathovar strains, which are associated with Crohn''s disease, share many genetic and phenotypic features with extraintestinal pathogenic E. coli (ExPEC) strains, but little is known about the level of genetic similarity between the two pathovars. We aimed to determine the frequency of strains with the “AIEC phenotype” among a collection of ExPEC strains and to further search for a common phylogenetic origin for the intestinal and extraintestinal AIEC strains. The adhesion, invasion, and intramacrophage replication capabilities (AIEC phenotype) of 63 ExPEC strains were determined. Correlations between virulence genotype and AIEC phenotype and between intestinal/extraintestinal origin, serotype, and phylogroup were evaluated for the 63 ExPEC and 23 intestinal AIEC strains. Phylogenetic relationships between extraintestinal and intestinal AIEC strains were determined using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis. Only four (6.35%) ExPEC strains, belonging to the O6:H1, O83:H1, and O25:H4 serotypes, were classified as having an AIEC phenotype. These strains were found to be genetically related to some intestinal AIEC strains of the same serotypes as revealed by MLST. No particular virulence gene sets correlated with the intestinal/extraintestinal origin of the strains or with the AIEC phenotype, whereas the gene sets did correlate with the serogroup. We identified two intestinal AIEC strains and one extraintestinal AIEC strain belonging to the O25:H4 serotype that also belonged to the emerging and virulent clonal group ST131. In conclusion, the ExPEC and AIEC pathovars share similar virulence gene sets, and certain strains are phylogenetically related. However, the majority of ExPEC strains did not behave like AIEC strains, thus confirming that the AIEC pathovar possesses virulence-specific features that, to date, are detectable only phenotypically.Members of the Enterobacteriaceae family, especially Escherichia coli, have been repeatedly suggested to play a role in the origin and/or perpetuation of Crohn''s disease (CD). In part, this suggestion was based on the higher abundance of this bacterium in CD patients than in control subjects (4, 10, 20, 23, 28, 29, 32, 41, 48, 51). Although considerable effort has been devoted to the search for intestinal pathogenic E. coli strains associated with CD, to date none of the six previously described pathovars (27) has been implicated in this condition. Darfeuille-Michaud et al. (18) observed that E. coli strains with adhesion and invasion properties colonized the ileal mucosae of CD patients more frequently than those of control subjects. Darfeuille-Michaud et al. further characterized these strains and proposed a new potential E. coli pathovar associated with CD, which was designated adherent-invasive E. coli (AIEC) (10). The implication of AIEC in CD is becoming increasingly relevant because several independent studies from different countries have reported a higher prevalence of invasive E. coli in CD patients (4, 17, 33, 34, 47).The main characteristics of AIEC are (i) the ability to adhere to and invade intestinal epithelial cells, (ii) the ability to survive and replicate expansively within macrophages without triggering host cell death and inducing the release of tumor necrosis factor alpha (21), and (iii) the lack of known invasive determinants (17). Recently, Glasser and Darfeuille-Michaud (22) proposed a model explaining the mechanism of pathogenesis for AIEC strains. The AIEC strains isolated to date are clonally diverse and belong to distinct serotypes. Moreover, despite the fact that they fall primarily into the B2 phylogroup, AIEC strains belonging to the A, B1, and D phylogroups have also been isolated (4, 33-35, 47). Although no specific virulence factors have been described for this pathovar, AIEC strains carry many virulence-associated genes characteristic of extraintestinal pathogenic E. coli (ExPEC) strains, which suggests that the AIEC pathovar could be closely related to the ExPEC pathovar (4, 17, 34).The aim of this work was to determine the frequency of strains with the “AIEC phenotype” among E. coli strains that cause extraintestinal infections, including uropathogenic E. coli (UPEC), septicemic E. coli, and neonatal meningitis E. coli strains. To achieve this objective, we determined the ability of a collection of ExPEC strains to adhere to and invade intestinal epithelial cells, as well as their capacity to survive and replicate within macrophages. In parallel, we compared the distributions of virulence-associated genes among ExPEC and AIEC strains. Furthermore, we searched for a common phylogenetic origin of the ExPEC strains that had an AIEC phenotype (referred to in this study as extraintestinal AIEC) and a collection of AIEC strains isolated mainly from the intestinal mucosae of CD patients (intestinal AIEC).     

Polynucleotide Sequence Relatedness Among Three Groups of Pathogenic Escherichia coli Strains

Escherichia coli strains that cause dysentery-like disease, parenteral infection, and infantile diarrhea form specific groups based on mobility of O and K antigens in immunoelectrophoresis. Members from each of these groups were assayed for gross nucleotide sequence relatedness. The method used was interspecific deoxyribonucleic acid (DNA) reassociation reactions carried out free in solution. Reassociated DNA was separated from unreacted DNA by passage through hydroxyapatite. DNA relatedness between these groups was approximately 80%. The groups containing those strains causing parenteral infection and those responsible for dysentery-like disease showed preferentially high intragroup DNA relatedness. The group containing strains responsible for infantile diarrhea did not show preferentially high intragroup DNA relatedness with the reference strain employed. These strains, however, did exhibit preferentially high DNA relatedness to a second reference strain.     

Mouse Virulence of Human, Systemic, Pathogenic Escherichia coli Strains

Strains of Escherichia coli isolated from systemic infections of humans exhibited marked intraperitoneal and intracerebral virulence for mice. This marked virulence was not exhibited by enteropathogenic strains.     

Sensitivity of polA mutants of Escherichia coli K-12 to ozone and radiations

Different polA mutants of Escherichia coli K-12 were exposedto ozone, X-rays and UV radiation, in order to compare the roleof the various enzymatic activities of DNA polymerase I in therepair of damage caused by these agents. As was the case withradiations, the polymerase-deficient mutants were the most sensitiveto ozone, followed by the 5'–3' exonuclease-deficientmutants. The 3'–5' exonuclease activity of pol I appearedto play a minor role in the repair of damage induced by allthese agents.     

Automated Ribotyping Provides Rapid Phylogenetic Subgroup Affiliation of Clinical Extraintestinal Pathogenic Escherichia coli Strains

Using the automated Riboprinter system, we have initiated the construction of an electronic Riboprint database composed of 72 ECOR reference strains and 15 archetypal virulent strains in order to provide a new simple molecular characterization method. More than 90% of the ECOR strains clustered in their original phylogenetic group. All but one of the archetypal virulent strains had a profile identical to that of one of the ECOR strains and could be easily affiliated with a phylogenetic group. This method appears to be an accurate and practical tool especially for investigating the genetic relationship between clinical extraintestinal pathogenic strains and B2 subgroup ECOR strains or archetypal pathotype strains.     

Plasmid-Borne Virulence-Associated Genes Have a Conserved Organization in Virulent Strains of Avian Pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) is an important respiratory pathogen of poultry. Various virulence factors are responsible for determining the pathogenicity of these strains, and it is commonly believed they are encoded on large plasmids the strains carry. This study examined a series of strains, the pathogenicity of which had previously been determined by aerosol exposure, for possession of large plasmids and found all isolates carried at least one large plasmid, regardless of the level of virulence. Virulence-associated genes carried on these plasmids were also examined, and it was shown that highly virulent strains carried at least four virulence-associated genes on their largest plasmid. Two of the virulence-associated genes were shown to be chromosomally located in a strain of intermediate virulence, while no virulence-associated genes were carried by the low-virulence strain. The organization of the virulence-associated genes was shown to be highly conserved among APEC isolates of high virulence, supporting the concept of a conserved portion of the putative virulence region that contributes to the pathogenicity of APEC strains.Avian pathogenic Escherichia coli (APEC) strains cause respiratory disease and septicemia in poultry and are economically important worldwide, causing significant mortality (13). The carriage of large plasmids is considered characteristic of APEC isolates (8), and pathogenicity is thought to be determined by virulence-associated factors encoded by them (15). These factors include serum resistance, encoded by the iss gene (14), temperature-sensitive hemagglutination, encoded by tsh (10), adhesins, the production of colicin V (ColV) and the possession of iron-scavenging mechanisms, such as aerobactin production (encoded by the iucABCD operon), and the more recently identified putative iron transport system encoded by the etsABC operon (18).Another iron acquisition system found in APEC utilizes salmochelin, a catecholate siderophore. The chromosomal iroA gene cluster that encodes this system was first found in Salmonella enterica (2) and is absent from the corresponding region of the E. coli chromosome (32), although it has been found on a transmissible plasmid from a uropathogenic E. coli isolate (34). The iroA gene cluster has been found on multiple APEC virulence plasmids (9, 17, 18, 37), and deletion studies have shown that the iroA gene cluster is required for full virulence (9).A further iron transport system, designated the sitABCD system, was first identified on a pathogenicity island in Salmonella enterica serovar Typhimurium (39), and it has been shown that sitABCD is required for full virulence of Salmonella serovar Typhimurium (16). Genomic subtraction identified the plasmid-located sitA gene from the sitABCD operon as unique to an APEC strain (32), and the sitA gene was found to be more prevalent in APEC than in commensal E. coli (18, 29, 32).The sitABCD operon occurs on APEC virulence plasmids (17, 18, 30, 37), but a sitABCD deletion mutant was still pathogenic for birds, suggesting that other iron transport systems are able to compensate for the loss of sitABCD (30).The carriage of ColV plasmids has previously been thought to be essential for virulence (3, 33, 38). However, other studies have suggested it is not the presence of the ColV gene itself but other genes that these plasmids carry that are responsible for virulence (28, 35). The well-characterized APEC virulence plasmids pAPEC-O2-ColV (18) and pAPEC-1 (9) encode ColV, while carriage of the Australian APEC virulence plasmid pVM01 does not confer production of ColV (12). Despite various ColV statuses, all three of these virulence plasmids are F-type plasmids, and hence this is potentially another way to characterize APEC virulence plasmids.SopA and SopB, which have similarity to the ParA and ParB proteins of the P1 plasmid, are thought to be essential for F-plasmid partitioning (22, 24). Detection of the genes of the sopABC locus could thus indicate the presence of a putative virulence plasmid.Strain E3 is an O-nontypeable:H28 APEC field isolate (11) that carries the 151-kb virulence plasmid pVM01 (12), which contains a virulence region with the virulence-associated genes iucA, tsh, iss, iroN, and sitA, as well as hlyF, ompT, and the etsABC operon (37). The arrangement of the virulence-associated genes around pVM01 (37) is similar to that in the plasmids pAPEC-O2-ColV from APEC strain O2 (18), pAPEC-O1-ColBM from APEC strain O1 (17), and pAPEC-1 from APEC strain χ7122 (23). Identifying a specific region that is conserved in highly virulent APEC strains will facilitate diagnosis of colibacillosis by differentiation of pathogenic strains from commensal E. coli and will also enable surveillance for pathogenic isolates in the environment of poultry.This study examined six E. coli strains, some of which were isolated from diseased birds and some of which were recovered from healthy birds (11, 36). The pathogenicity of these strains has been determined using aerosol exposure (11, 36), making this the largest known collection of APEC strains fulfilling Koch''s postulates. The series of strains includes the highly virulent strains E3, E30, and E956 and the less-virulent strains E133, E1043, and E1292. The presence of the virulence-associated genes iucA, tsh, and iss in these strains has previously been elucidated by PCR amplification (36). However, while previous studies have found many of these virulence factors to be encoded by APEC strains associated with disease (29) and have suggested that they are encoded on virulence plasmids (18), they have not conclusively determined whether they are encoded on virulence plasmids or are chromosomally encoded. Similarly, although previous studies suggest that these virulence-associated genes are consistently present in isolates from diseased birds (1, 6, 18, 21, 26, 29), no study has yet determined if these genes are consistently associated with each other.The aim of this study was to examine a series of strains of known pathogenicities for the possession of large plasmids and to determine if known virulence-associated genes from the putative virulence region were carried on them. The second objective was to investigate any association between the virulence-associated genes.     

Phagocytic resistance of Escherichia coli K-1 isolates and relationship to virulence.

Blood culture isolates from 133 episodes of Escherichia coli bacteremia were typed for K-1 capsular antigen by immunodiffusion, utilizing equine antiserum raised against meningococcal group B polysaccharide. Twenty-six percent (34 of 133) of these isolates were positive for K-1 antigen. These 133 strains, 34 K-1 and 99 non-K-1, were tested for susceptibility to phagocytosis. K-1 strains were found to be more resistant to clearance (27%) than non-K-1 strains (71%) when tested in an in vitro opsonophagocytic/killing assay containing normal human granulocytes and plasma. Additional studies demonstrated that resistance was due to decreased phagocytosis rather than diminished intraleukocytic killing. K-1 strains obtained from stool showed a similar degree of resistance to phagocytosis when compared with K-1 blood isolates. A comparison of clinical data on non-neonatal patients with E. coli K-1 and non-K-1 bacteremia showed no significant differences in mortality for these two groups. The incidence of shock for patients bacteremic with K-1 strains (74%) was significantly greater than that for patients bacteremic with non-K-1 strains (33%). These differences are attributed to the increased resistance to phagocytosis observed for K-1 versus non-K-1 E. coli isolates.     

Sequencing and Functional Annotation of Avian Pathogenic Escherichia coli Serogroup O78 Strains Reveal the Evolution of E. coli Lineages Pathogenic for Poultry via Distinct Mechanisms

Avian pathogenic Escherichia coli (APEC) causes respiratory and systemic disease in poultry. Sequencing of a multilocus sequence type 95 (ST95) serogroup O1 strain previously indicated that APEC resembles E. coli causing extraintestinal human diseases. We sequenced the genomes of two strains of another dominant APEC lineage (ST23 serogroup O78 strains χ7122 and IMT2125) and compared them to each other and to the reannotated APEC O1 sequence. For comparison, we also sequenced a human enterotoxigenic E. coli (ETEC) strain of the same ST23 serogroup O78 lineage. Phylogenetic analysis indicated that the APEC O78 strains were more closely related to human ST23 ETEC than to APEC O1, indicating that separation of pathotypes on the basis of their extraintestinal or diarrheagenic nature is not supported by their phylogeny. The accessory genome of APEC ST23 strains exhibited limited conservation of APEC O1 genomic islands and a distinct repertoire of virulence-associated loci. In light of this diversity, we surveyed the phenotype of 2,185 signature-tagged transposon mutants of χ7122 following intra-air sac inoculation of turkeys. This procedure identified novel APEC ST23 genes that play strain- and tissue-specific roles during infection. For example, genes mediating group 4 capsule synthesis were required for the virulence of χ7122 and were conserved in IMT2125 but absent from APEC O1. Our data reveal the genetic diversity of E. coli strains adapted to cause the same avian disease and indicate that the core genome of the ST23 lineage serves as a chassis for the evolution of E. coli strains adapted to cause avian or human disease via acquisition of distinct virulence genes.     

Pathogenic strains of Escherichia coli in Taiwan

From July 1994 through June 1996, 28 strains of Escherichia coli were isolated from 1,260 patients with acute diarrhea. These strains were further differentiated with serotypes and virulence factors. Enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), and enteroinvasive E. coli (EIEC) were accounted for 53.6 (15 of 28 strains), 28.6 (8 of 28), 10.7 (3 of 28) and 7.1% (2 of 28), respectively. Therefore, ETEC and EPEC are playing an important role in food-borne illness in Taiwan. Escherichia coli O157:H7, a new emerging pathogen of food-borne disease, has not been isolated in this study.     

High Thiobarbiturate-Positive O Antigen of Escherichia coli

A degraded antigen containing a large amount of thiobarbiturate-reactive material, and distinguishable from the acetic acid-degraded polysaccharide antigen, was obtained by phenol extraction of a Boivin antigen.     

Novel intergenic repeats of Escherichia coli K-12

An online catalog of intergenic DNA repeat sequence elements is added to the EcoGene Escherichia coli K-12 genome sequence annotation and analysis project (bmb.med.miami.edu/EcoGene). A library of noncoding (intergenic) DNA sequences depleted of known intergenic repeat classes was searched for DNA sequence similarities to identify novel DNA repeat sequence classes.     

Type 1 Fimbriation and Its Phase Switching in Diarrheagenic Escherichia coli Strains

Type 1 fimbriae can be expressed by most Escherichia coli strains and mediate mannose-sensitive (MS) adherence to mammalian epithelial cells. However, the role of type 1 fimbriae in enteric pathogenesis has been unclear. Expression of type 1 fimbriae in E. coli is phase variable and is associated with the inversion of a short DNA element (fim switch). Forty-six strains of diarrheagenic E. coli were examined for the expression of type 1 fimbriae. Only four of these strains were originally type 1 fimbriated. Seventeen strains, originally nonfimbriated, expressed type 1 fimbriae in association with off-to-on inversion of the fim switch, after serial passages in static culture. The switching frequencies of these strains, from fimbriate to nonfimbriate, were greater than that of the laboratory strain E. coli K-12. None of the 16 strains of serovar O157:H7 or O157:H⁻ expressed type 1 fimbriae after serial passages in static culture. The nucleotide sequence analysis of the fim switch region revealed that all of the O157:H7 and O157:H⁻ strains had a 16-bp deletion in the invertible element, and the fim switch was locked in the “off” orientation. The results suggest that expression of type 1 fimbriae may be regulated differently in different E. coli pathogens causing enteric infections.     

Cyclomodulins in Urosepsis Strains of Escherichia coli

Determinants of urosepsis in Escherichia coli remain incompletely defined. Cyclomodulins (CMs) are a growing functional family of toxins that hijack the eukaryotic cell cycle. Four cyclomodulin types are actually known in E. coli: cytotoxic necrotizing factors (CNFs), cycle-inhibiting factor (Cif), cytolethal distending toxins (CDTs), and the pks-encoded toxin. In the present study, the distribution of CM-encoding genes and the functionality of these toxins were investigated in 197 E. coli strains isolated from patients with community-acquired urosepsis (n = 146) and from uninfected subjects (n = 51). This distribution was analyzed in relation to the phylogenetic background, clinical origin, and antibiotic resistance of the strains. It emerged from this study that strains harboring the pks island and the cnf1 gene (i) were strongly associated with the B2 phylogroup (P, <0.001), (ii) frequently harbored both toxin-encoded genes in phylogroup B2 (33%), and (iii) were predictive of a urosepsis origin (P, <0.001 to 0.005). However, the prevalences of the pks island among phylogroup B2 strains, in contrast to those of the cnf1 gene, were not significantly different between fecal and urosepsis groups, suggesting that the pks island is more important for the colonization process and the cnf1 gene for virulence. pks- or cnf1-harboring strains were significantly associated with susceptibility to antibiotics (amoxicillin, cotrimoxazole, and quinolones [P, <0.001 to 0.043]). Otherwise, only 6% and 1% of all strains harbored the cdtB and cif genes, respectively, with no particular distribution by phylogenetic background, antimicrobial susceptibility, or clinical origin.The bacterial species Escherichia coli comprises a wide diversity of strains belonging to the commensal intestinal flora of humans and warm-blooded animals. Among these strains, several pathogenic variants cause intestinal or extraintestinal infections in humans and animals (33). Population genetic studies based on multilocus enzyme electrophoresis and various DNA markers (10, 20, 44) classify the E. coli strains into four major phylogenetic groups (A, B1, B2, and D). The groups are diversely associated with certain ecological niches and propensities to cause disease.Extraintestinal pathogenic E. coli (ExPEC) strains are facultative pathogens that are not yet fully described. They are reported to belong mainly to phylogroups B2 and D, and they possess high numbers of virulence genes that belong to a flexible gene pool (43, 53). Among ExPEC strains, uropathogenic E. coli (UPEC) strains take advantage of host behavior and susceptibility by employing virulence factors that facilitate bacterial growth and persistence in the urinary tract (5, 28-30). Important virulence mechanisms are adhesion, invasion, subversion of host defenses, and direct interference with host cellular functions via secreted effectors (33, 69).These effectors include the cyclomodulins (CMs), a functional class of toxins that hijack the cell cycle, a fundamental host cell process (48). In the species E. coli, four kinds of CMs have been identified: the rho GTPase-targeting toxins CNF-1 to CNF-3 (cytotoxic necrotizing factors) (34), the cycle-inhibiting factor (Cif) (38), and two kinds of genotoxins, cytolethal distending toxins (CDTs) I to V (19) and the recently discovered colibactin (41). Colibactin is probably a hybrid polyketide-nonribosomal peptide toxin, whose activity is encoded by the genomic pks island (41). CDTs, Cif, and colibactin block mitosis, whereas CNFs promote DNA replication without cytokinesis. CM production can therefore be detected by the analysis of the cytopathic effects induced (41, 50).E. coli CMs are encoded by mobile elements (genomic islands, plasmids, and bacteriophages) that belong to the flexible gene pool of E. coli (22). The aim of the present study was to compare the prevalences of CMs in E. coli strains that differed in their clinical origins (community-acquired urosepsis or feces), phylogroups, and susceptibilities to antimicrobial agents.     

Epidemiology and Clinical Manifestations of Enteroaggregative Escherichia coli

SUMMARY

Enteroaggregative Escherichia coli (EAEC) represents a heterogeneous group of E. coli strains. The pathogenicity and clinical relevance of these bacteria are still controversial. In this review, we describe the clinical significance of EAEC regarding patterns of infection in humans, transmission, reservoirs, and symptoms. Manifestations associated with EAEC infection include watery diarrhea, mucoid diarrhea, low-grade fever, nausea, tenesmus, and borborygmi. In early studies, EAEC was considered to be an opportunistic pathogen associated with diarrhea in HIV patients and in malnourished children in developing countries. In recent studies, associations with traveler''s diarrhea, the occurrence of diarrhea cases in industrialized countries, and outbreaks of diarrhea in Europe and Asia have been reported. In the spring of 2011, a large outbreak of hemolytic-uremic syndrome (HUS) and hemorrhagic colitis occurred in Germany due to an EAEC O104:H4 strain, causing 54 deaths and 855 cases of HUS. This strain produces the potent Shiga toxin along with the aggregative fimbriae. An outbreak of urinary tract infection associated with EAEC in Copenhagen, Denmark, occurred in 1991; this involved extensive production of biofilm, an important characteristic of the pathogenicity of EAEC. However, the heterogeneity of EAEC continues to complicate diagnostics and also our understanding of pathogenicity.     

Uridinediphosphogalactose-4-Epimerase Deficiency in Salmonella typhimurium and Its Correction by Plasmid-Borne Galactose Genes of Escherichia coli K-12: Effects on Mouse Virulence, Phagocytosis, and Serum Sensitivity

The synthesis of smooth lipopolysaccharide (LPS) in relation to mouse virulence and resistance to serum bactericidal activity in vitro and to rapid intravenous clearance in vivo was studied in Salmonella typhimurium by using a virulent [median lethal dose (LD₅₀) = 10²], smooth, and genetically marked strain, a uridinediphosphogalactose epimerase-deficient mutant of it which was, therefore, rough, and a derivative of the mutant made smooth again by acquisition of the galactose-positive genes of Escherichia coli. The mutant was of reduced virulence (LD₅₀ = 10⁶) but the smooth derivative regained the virulence character typical of the parent. The non-smooth phenotype also made the mutant, but not the smooth relatives (parent and derivative), susceptible to serum bactericidal activity and also to rapid intravenous clearance by phagocytosis by the liver. The mutant was similarly treated by germ-free mice (expected to be relatively free of opsonizing antibodies). The clearance of the mutant could be impaired by prior intravenous inoculation of homologous bacteria or their LPS but was reversible by preopsonization of the second inoculum with nonimmune mouse serum, suggesting that the initial inoculum preempted the opsonizing antibodies. Independent evidence of clearance specificity was also provided in mixed inoculum experiments on impaired mice by the rapid clearance of an antigenically unrelated heptose-deficient mutant while maintaining the decelerated clearance of the epimerase mutant. The latter, however, was converted to accelerated clearance by the intravenous inoculation during the impaired state of anti-epimerase mutant immune mouse serum.