The traditional enteropathogenic Escherichia coli (EPEC) serogroup O125 comprises serotypes which are mainly associated with the category of enteroaggregative E. coli

Structural elucidation of the O-antigen polysaccharide from Escherichia coli O125ac and biosynthetic aspects thereof

Enteropathogenic Escherichia coli O125, the cause of infectious diarrheal disease, is comprised of two serogroups, viz., O125ab and O125ac, which display the aggregative adherence pattern with epithelial cells. Herein, the structure of the O-antigen polysaccharide from E. coli O125ac:H6 has been elucidated. Sugar analysis revealed the presence of fucose, mannose, galactose and N-acetyl-galactosamine as major components. Unassigned 1H and 13C NMR data from one- and two-dimensional NMR experiments of the O125ac O-antigen in conjunction with sugar components were used as input to the CASPER program, which can determine polysaccharide structure in a fully automated way, and resulted in the following branched pentasaccharide structure of the repeating unit: →4)[β-d-Galp-(1 → 3)]-β-d-GalpNAc-(1 → 2)-α-d-Manp-(1 → 3)-α-l-Fucp-(1 → 3)-α-d-GalpNAc-(1→, where the side chain is denoted by square brackets. The proposed O-antigen structure was confirmed by 1H and 13C NMR chemical shift assignments and determination of interresidue connectivities. Based on this structure, that of the O125ab O-antigen, which consists of hexasaccharide repeating units with an additional glucosyl group, was possible to establish in a semi-automated fashion by CASPER. The putative existence of gnu and gne in the gene clusters of the O125 serogroups is manifested by N-acetyl-d-galactosamine residues as the initial sugar residue of the biological repeating unit as well as within the repeating unit. The close similarity between O-antigen structures is consistent with the presence of two subgroups in the E. coli O125 serogroup.

Secreted autotransporter toxin (Sat) induces cell damage during enteroaggregative Escherichia coli infection

Secreted autotransporter toxin (Sat) is a 107-kDa serine protease autotransporter of Enterobacteriaceae (SPATE) presenting cytotoxic activity in renal and bladder cells. Further studies have detected the Sat-encoding gene (sat) in enteroaggregative Escherichia coli (EAEC) and in E. coli strains isolated from neonatal septicemia and meningitis. Here, we investigated the role of Sat as a cytotoxin of EAEC. Sat was purified from a strain of E. coli harboring sat (DEC/Sat+, O126:H2) and used to raise antibodies in rabbit. The presence of Sat was detected by ELISA in the supernatant of 93.7% of EAEC strains harboring sat and in none lacking the gene. The effect of Sat during infection was investigated in polarized Caco-2 cells infected with Sat-producing EAEC (CV323/77, O125ab:H21). This strain induced intense cell detachment, which was inhibited by PMSF or Sat antiserum. Also, sat transcription and Sat production were detected during infection. Here we demonstrate that Sat is internalized in polarized cells leading to F-actin disruption which preceded cell detachment. A comparative study of the toxin action in cell lines corresponding to the infection sites in which bacteria carrying the sat gene have been isolated was performed. Cells originating from the gastrointestinal tract (Caco-2), urinary (LLC-PK1) and endothelium (HUVEC) were incubated with purified Sat. The time required for observation of cell damage differed according to the cell line. HUVEC cells were more sensitive to Sat than cells derived from urinary and intestinal tracts. The intense activity of Sat on the endothelial cells suggests that Sat could also be a virulence factor for the bacteria in the bloodstream. In addition, this is the first work demonstrating that Sat induces cytotoxic effect during EAEC infection in vitro. The cell damage observed during infection indicates that Sat may be another toxin with cytotoxic role in the EAEC pathogenesis.

Adhesins of Enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) strains induce morphological changes in infected epithelial cells. The resulting attaching and effacing (A/E) lesion is characterized by intimate bacterial adherence to epithelial cells, with microvillus destruction, cytoskeletal rearrangement, and aggregation of host cytoskeletal proteins. This review presents an overview of the adhesion mechanisms used for the colonization of the human gastrointestinal tract by EPEC. The mechanisms underlying EPEC adhesion, prior to and during the formation of the A/E lesion, and the host cytosolic responses to bacterial infection leading to diarrheal disease are discussed.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Clonal relationship among atypical enteropathogenic Escherichia coli strains isolated from different animal species and humans

Forty-nine typical and atypical enteropathogenic Escherichia coli (EPEC) strains belonging to different serotypes and isolated from humans, pets (cats and dogs), farm animals (bovines, sheep, and rabbits), and wild animals (monkeys) were investigated for virulence markers and clonal similarity by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The virulence markers analyzed revealed that atypical EPEC strains isolated from animals have the potential to cause diarrhea in humans. A close clonal relationship between human and animal isolates was found by MLST and PFGE. These results indicate that these animals act as atypical EPEC reservoirs and may represent sources of infection for humans. Since humans also act as a reservoir of atypical EPEC strains, the cycle of mutual infection of atypical EPEC between animals and humans, mainly pets and their owners, cannot be ruled out since the transmission dynamics between the reservoirs are not yet clearly understood.

Domestic cats constitute a natural reservoir of human enteropathogenic Escherichia coli types

Feces of 70 diarrhoeic and 230 non-diarrhoeic domestic cats from Sao Paulo, Brazil were investigated for enteropathogenic (EPEC), enterohaemorrhagic (EHEC) and enterotoxigenic (ETEC) Escherichia coli types. While ETEC and EHEC strains were not found, 15 EPEC strains were isolated from 14 cats, of which 13 were non-diarrhoeic, and one diarrhoeic. None of 15 EPEC strains carried the bfpA gene or the EPEC adherence factor plasmid, indicating atypical EPEC types. The EPEC strains were heterogeneous with regard to intimin types, such as eae-theta (three strains), eae-kappa (n = 3), eae-alpha1 (n = 2), eae-iota (n = 2), one eae-alpha2, eae-beta1 and eae-eta each, and two were not typeable. The majority of the EPEC isolates adhered to HEp-2 cells in a localized adherence-like pattern and were positive for fluorescence actin staining. The EPEC strains belonged to 12 different serotypes, including O111:H25 and O125:H6, which are known to be pathogens in humans. Multi locus sequence typing revealed a close genetic similarity between the O111:H25 and O125:H6 strains from cats, dogs and humans. Our results show that domestic cats are colonized by EPEC, including serotypes previously described as human pathogens. As these EPEC strains are also isolated from humans, a cycle of mutual infection by EPEC between cats and its households cannot be ruled out, though the transmission dynamics among the reservoirs are not yet understood clearly.

Molecular typing and virulence of enteroaggregative Escherichia coli strains isolated from children with and without diarrhoea in Rio de Janeiro city, Brazil

Enteroaggregative Escherichia coli (EAEC) strains have been implicated as emerging aetiological agents of diarrhoea worldwide. In the present study, 43 EAEC strains were serotyped and characterized according to random amplification of polymorphic DNA profiles, PFGE, multilocus enzyme electrophoresis (MLEE) and the presence of putative virulence genes (hly, aero, kps, fim, aggA, aafA, aggR, astA, she, aap, shf and pet). The EAEC strains consisted of a diversity of serotypes including eight O-non-typable and 35 O-typable strains arranged into 21 O : H combinations. Amplification of specific genes revealed that all strains carried at least two of the virulence sequences investigated. fim, aggR and aap were the most frequent genes in both groups studied. hly, aero and aggA sequences were more prevalent in the diarrhoeal group. kps occurred exclusively in strains isolated from symptomatic children and showed strong association with diarrhoeal disease. The molecular approaches used to investigate the relatedness among EAEC strains revealed a high degree of polymorphism, suggesting that these micro-organisms have a non-clonal origin. A closer relationship was observed among EAEC strains sharing O : H types. No significant clustering could be identified related to the virulence traits investigated; however, the she locus showed clonal distribution by MLEE typing. These results are in accordance with previous findings in revealing the conservation of particular EAEC factors, despite the high degree of diversity related to both genotypic and phenotypic markers.

Escherichia coli O125ac:H6 encompasses atypical enteropathogenic E. coli strains that display the aggregative adherence pattern

O125 is an enteropathogenic Escherichia coli (EPEC) serogroup, which includes the O125ac:H6 serotype, defined as atypical EPEC. Strains of this serotype displayed the aggregative adherence (AA) pattern with HEp-2, Caco-2, T84, and HT-29 cells, possessed all the LEE region genes, and expressed intimin, Tir, and EspABD, although the attaching-effacing lesion was not detected in vitro. These results confirm that E. coli O125ac:H6 is atypical EPEC that displays the AA pattern and indicate the necessity of testing for EPEC genes combined with the determination of the adherence pattern for atypical EPEC identification.

Genetic relationship of diarrheagenic Escherichia coli pathotypes among the enteropathogenic Escherichia coli O serogroup

The genetic relationship among the Escherichia coli pathotypes was investigated. We used random amplified polymorphic DNA (RAPD) data for constructing a dendrogram of 73 strains of diarrheagenic E. coli. A phylogenetic tree encompassing 15 serotypes from different pathotypes was constructed using multilocus sequence typing data. Phylogram clusters were used for validating RAPD data on the clonality of enteropathogenic E. coli (EPEC) O serogroup strains. Both analyses showed very similar topologies, characterized by the presence of two major groups: group A includes EPEC H6 and H34 strains and group B contains the other EPEC strains plus all serotypes belonging to atypical EPEC, enteroaggregative E. coli (EAEC) and enterohemorrhagic E. coli (EHEC). These results confirm the existence of two evolutionary divergent groups in EPEC: one is genetically and serologically very homogeneous whereas the other harbors EPEC and non-EPEC serotypes. The same situation was found for EAEC and EHEC.

Diarrheagenic Escherichia coli categories among the traditional enteropathogenic E. coli O serogroups--a review

The so called enteropathogenic Escherichia coli (EPEC) O serogroups include typical and atypical EPEC, enterohaemorrragic E. coli, enterotoxigenic E. coli, and enteroaggregative E. coli. The aim of this article is to review the composition of each O serogroup and the major serotypes, clones, and additional virulence characteristics of each of these diarrheagenic categories. Their adherence patterns and genetic relationships are also presented. The review is based on the study of 805 strains of serogroups O26, O55, O86, O111, O114, O119, O125, O126, O1127, O128, and O142 most of which isolated in Sao Paulo from children with diarrhea between 1970 and 1990. Since some O serogroups include more than one diarrheagenic category O serogrouping only should be abandoned as a diagnostic method. However serotyping is a reliable method for those serotypes that correspond to clones.

Frequency and characteristics of diarrhoeagenic Escherichia coli strains isolated from children with and without diarrhoea in Rio de Janeiro, Brazil

The frequency of diarrhoeagenic Escherichia coli (DEC) strains was investigated in 253 children up to 3 years old, with (patient group, PG, 199 children) and without (control group, CG, 54 children) diarrhoea, living in Rio de Janeiro, Brazil. DEC strains were detected in 70 (27.6%) children, including 54 (27.1%) with diarrhoea and 16 (29.6%) without diarrhoea. Enteroaggregative E. coli (EAEC) was the most frequent DEC category, accounting for 14.6% of the isolates in the PG and for 11.1% in the CG. E. coli strains carrying enteropathogenic E. coli (EPEC) virulence markers showed higher incidence in the CG (12.9%) than in the PG (8.0%). E. coli strains belonging to non-classical EPEC groups that carried eae only or eae and bfpA, designated as attaching-effacing E. coli (AEEC) were the most frequent (79.1%). Simultaneous presence of multiple EPEC virulence factors (EAF/eae/bfpA) were only detected among strains isolated from the PG. Enterotoxigenic E. coli (ETEC) strains were isolated from 5.5% of the children in the CG and from 3.5% of those in the PG. Most of the ETEC isolates were LT-probe positive (70%) and none carried both LT-I and ST-I probe sequences. One enteroinvasive E. coli (EIEC) strain was recovered from a child with diarrhoea. No stx-probe positive E. coli strains were detected. Overall, DEC strains were not found to be significantly associated with diarrhoea (p>0.05). However, the higher incidence of EAEC, the most frequent DEC category, among children with diarrhoea, suggests a potential role of EAEC as an important enteric pathogen in the community investigated.

Virulence markers of enteroaggregative Escherichia coli isolated from children and adults with diarrhea in Brasília, Brazil

Escherichia coli strains isolated from sporadic cases of acute diarrhea in children and adults and from children without diarrhea were investigated for the presence of the pAA plasmid. Strains harboring the pAA plasmid were isolated at similar frequencies from children with (19.6%) and without (10.8%) diarrhea and from adults with diarrhea (11.8%). The genotypic and phenotypic virulence markers of these strains were further analyzed. Most of the strains were positive for EAST1 (73%), and this toxin was detected significantly more frequently in strains from children with diarrhea than in strains from adults with diarrhea (P < 0.05). Likewise, pic sequences were detected significantly more frequently in strains from children with diarrhea than in strains from adults with diarrhea (P < 0.005) and controls (P < 0.025). Furthermore, the association of pAA positivity (pAA(+)) and pic positivity (pic(+)) was more frequently found for strains from children with diarrhea than for strains from controls, indicating that pAA(+) pic(+) strains may represent a subset of pAA(+) strains associated with disease in children. Most of the strains (82.5%) adhered to cells presenting the typical aggregative pattern. The frequency of occurrence of enteropathogenic E. coli (EPEC) serogroups in the strains from children with diarrhea was very high (56%), while none of the strains from adults with diarrhea belonged to EPEC serogroups. Extraintestinal virulence markers were very commonly found in strains from adults with diarrhea. The frequencies of occurrence of the adhesins AFA and SFA were significantly higher in strains from adults with diarrhea than in strains from children with diarrhea. More than one extraintestinal virulence marker was found in 58% of the strains from adults with diarrhea but in only 7.7% of the strains from children with diarrhea. Our results show that pAA(+) strains isolated from children and adults with diarrhea present very different profiles when enteroaggregative E. coli virulence markers, serotypes, and extraintestinal virulence markers are considered.

Typical and atypical enteropathogenic Escherichia coli

Typical and atypical enteropathogenic Escherichia coli (EPEC) strains differ in several characteristics. Typical EPEC, a leading cause of infantile diarrhea in developing countries, is rare in industrialized countries, where atypical EPEC seems to be a more important cause of diarrhea. For typical EPEC, the only reservoir is humans; for atypical EPEC, both animals and humans can be reservoirs. Typical and atypical EPEC also differ in genetic characteristics, serotypes, and virulence properties. Atypical EPEC is more closely related to Shiga toxin-producing E. coli (STEC), and like STEC these strains appear to be emerging pathogens.

An enteroaggregative Escherichia coli strain of serotype O111:H12 damages and invades cultured T84 cells and human colonic mucosa

The pathogenic mechanisms of enteroaggregative Escherichia coli (EAEC) are not well defined. We investigated the interaction of EAEC strain 236 (serotype O111:H12) with polarised Caco-2 and T84 human intestinal epithelial cells lines, and with human jejunal and colonic mucosa. Strain 236 adhered to both polarised cell lines and to both intestinal tissue types, but caused severe damage and was invasive only in T84 cells and colonic mucosa. In contrast, prototype EAEC strain 042, which also adhered to the cultured intestinal cell lines, did not adhere to or invade jejunal or colonic tissue. These observations suggest a heterogeneity of virulence properties within the EAEC category of diarrhoea-causing E. coli.

Production of cytolethal distending toxin and other virulence characteristics of Escherichia coli strains of serogroup O86

Genetic and phenotypic virulence markers of different categories of diarrhoeagenic Escherichia coli were investigated in 106 strains of enteropathogenic E. coli (EPEC) serogroup O86. The most frequent serotype found was O86:H34 (86%). Strains of this serotype and the non motile ones behaved as EPEC i.e., carried eae, bfpA and EAF DNA sequences and presented localised adherence to HeLa cells. Serotypes O86:H2, O86:H6, O86:H10, O86:H18, O86:H27 and O86:H non determined, belonged to other categories. The majority of the strains of serotype O86:H34 and non motile strains produced cytolethal-distending toxin (CDT). The ribotyping analysis showed a correlation among ribotypes, virulence markers and serotypes, thus suggesting that CDT production might be a property associated with a universal clone represented by the O86:H34 serotype.