Examination of strains belonging to enteropathogenic Escherichia coli serogroups for genes encoding EPEC adherence factor and Vero cytotoxins

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.

Distribution and expression of the astA gene (EAST1 toxin) in Escherichia coli and Salmonella

The distribution and expression of the astA gene (EAST1 toxin) among 358 strains of Enterobacteriaceae were studied. The gene was found in 32.6% and 11.9% of Escherichia coli and Salmonella strains, respectively. The majority of E. coli EAST1-positive strains were found among EHEC (88.0%), EAggEC (86.6%), and A-EPEC (58.3%). The gene was present in 16.6% of E. coli strains without known virulence genes. There was no significant variation among the different serotypes of E. coli tested regarding the presence of the gene. For EPEC, 13.7% of the tested strains were astA-positive. Among atypical EPEC (eae+, bfp-, EAF-) and (eae+, bfp+, EAF-) 46.2 and 72.7%, respectively, were positive. The majority of the A-EPEC (87%) and EaggEC (83%) strains expressed the EAST-1 toxin as judged from Ussing chamber experiments. Of 32 EIEC strains studied, 2 possessed and expressed the gene as determined in Ussing chamber experiments. Among the Salmonella strains studied, five strains isolated from food were positive for astA and one strain of S. agona showed biological activity in Ussing chamber experiments.

Virulence-related DNA sequences and adherence patterns in strains of enteropathogenic Escherichia coli

The presence of the genes for Escherichia coli adherence factor (EAF), attaching and effacing lesion (eae) and bundle-forming pili (bfp) in 72 strains identified as enteropathogenic E. coli (EPEC) by slide agglutination was evaluated using hybridization and PCR. The adherence property of these strains was assayed using 3h HeLa cells adherence assay. The results obtained indicated that virulence-associated genes were present in 65% of the strains but only ten (13.9%) isolates were positive for all the three markers (typical EPEC), 37 (51.4%) isolates carried either one or two of these determinants (atypical EPEC) and the remaining 25 (34.7%) were negative for all these genes. In vitro adherence assay showed that 44 (61.1%) strains adhered to HeLa cells with a defined pattern, 13 (18.1%) isolates adhered loosely with no definite pattern and the remaining 15 (20.8%) were non-adherent. Analysis of the results showed a statistically significant association between the presence of the virulence-related genes with adherence of the strains with a defined pattern (P</=0.0001). These results indicated that since over 60% of the strains identified by serogrouping carried at least one of the putative virulence markers, it therefore seems that this simple test is still of value in our setting although the need for a confirmatory test is also indicated.

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

Genotypic and phenotypic virulence markers of the different categories of diarrheagenic Escherichia coli were investigated in 76 strains of the enteropathogenic E. coli (EPEC) serogroup O125. The most frequent serotype found was O125ac:H21. None of the serotypes behaved as EPEC, i.e. carried the eaeA, bfpA, and EAF DNA sequences simultaneously and presented localized adherence to HeLa cells. All strains of O125ac:H6 were atypical EPEC since they carried eaeA only, and presented an indefinite pattern of adherence. All strains of O125ab:H9, O125ac:H9, O125?:H16, and O125ab:H21 and 79% of the O125ac:H21 strains were enteroaggregative E. coli, since they carried a specific DNA sequence and presented the typical aggregative adherence pattern.

Virulence properties of Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups isolated from calves with diarrhea

Nineteen Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups were isolated from calves with diarrhea in Paraná State. Brazil, and studied for virulence markers associated with EPEC or enterohemorrhagic E. coli (EHEC). The 19 isolates belonged to 12 serotypes with isolates of O26:H11, O119:H25 and O114:H- being the most prevalent Localized adherence (LA) was demonstrated for 37% of the isolates, consisting of all four O26:H11, both O114:H- and one O114:H40 isolates. All the LA strains were positive in the fluorescent-actin staining (FAS) test and possessed attaching-effacing E. coli (eae) sequences, but only O114 strains hybridized with the EPEC adherence factor (EAF) probe. None of the strains produced Shiga-like toxins (Verotoxin). Only the O26:H11 strains hybridized with the EHEC plasmid specific (CVD419) probe and were enterohemolytic, properties associated with EHEC strains. This investigation demonstrates that among the bovine strains isolated only those of serogroup O114 behaved as typical EPEC.

Characteristics of Escherichia coli strains belonging to enteropathogenic E. coli serogroups isolated in Italy from children with diarrhea

Fifty-five Escherichia coli strains belonging to enteropathogenic E. coli (EPEC) serogroups were examined for phenotypic and genetic factors associated with virulence. The strains were isolated in Italy from children with diarrhea and identified as EPEC by clinical laboratories using commercially available antisera. O:H serotyping showed that 35 strains (27 of O26, O111, and O128 serogroups) belonged to 11 serotypes considered to be classical EPEC O:H serotypes. The other 20 isolates were classified as 15 nonclassical EPEC O:H serotypes. All the potential EPEC virulence factors associated with bacterial adhesion (localized adherence, fluorescentactin staining test positivity, presence of the attaching and effacing [eaeA] gene), the production of verotoxin, and the positivity with the enterohemorrhagic E. coli probe were significantly more frequent among isolates belonging to classical than nonclassical serotypes. Strains displaying an aggregative adhesion and hybridizing with the enteroaggregative DNA probe were found in serogroups O86, O111, and O126. Verotoxin-producing isolates belonged to serogroups O26, O111, and O128. Only one of the isolates hybridized with the EPEC adherence factor (EAF) probe, but 33 strains gave positive results with the eae probe, confirming that the former is more suitable in epidemiological studies in European countries. These results indicate that up to 75% of strains identified as EPEC by commercial antisera may possess potential virulence properties and/or belong to classical EPEC O:H serotypes and suggest that O grouping is still a useful diagnostic tool for presumptive identification of diarrheagenic E. coli in clinical laboratories.

Adherence patterns and DNA probe types of Escherichia coli isolated from diarrheal patients in China

One hundred and seventy-two strains of Escherichia coli isolated from diarrheal patients in Beijing, P.R. China, were analyzed for plasmid DNA profile, HEp-2 cell adherence ability and reactivity to 10 previously described DNA probes. They had not been recognized as pathogenic E. coli in China. Of the 110 strains tested, 76 (69%) contained one or multiple large plasmids. Of the 71 strains with the large plasmids 64 could adhere to HEp-2 cells. Of the 172 strains, 102 (59.3%) were hybridized with at least one of the 10 probes. Of those, seven strains hybridized with enteroaggregative E. coli (EAggEC) probe. Their serotypes were O128 (two strains), O6 (one strain), and O111 (one strain). Three strains were untypable. Six and three strains were hybridized with enteropathogenic E. coli (EPEC) attaching and effacing genes (eae) or EPEC adherence factor (EAF) probe, respectively. Two non-O157: H7 strains hybridized with enterohemorrhagic E. coli (EHEC) probe. Seventy-two strains (41.9%) hybridized with shiga-like toxin 2 or 1 (SLT2 or SLT1) probes. Among the SLT1 or SLT2 probe-positive strains, 54 hybridized with invasive (INV) plasmid probe developed for identification of enteroinvasive E. coli (EIEC) and Shigella species. The INV and SLT probe-positive strains might represent a new variety of verotoxin-producing E. coli (VTEC).

Adhesion and its role in the virulence of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) organisms are an important cause of diarrheal disease in young children. The virulence of EPEC is a multifactorial process and involves a number of distinct stages. Initial adherence to intestinal mucosa is mediated by fimbriae which bring about a distinct form of adhesion, localized adhesion. Intimate adhesion of the bacterium to the eukaryotic membrane occurs, resulting in the activation of signal transduction pathways. Microvilli are disrupted and effaced from the apical membrane which then cups around the organism to form pedestal structures, the attaching and effacing lesion. Diarrhea may be produced by alteration of the permeability of the apical membrane and also through a malabsorption mechanism. The pathways involved in the production of the attaching and effacing lesion are described. EPEC organisms were originally thought to belong to a number of distinct serogroups; it is now apparent that many isolates belonging to these serogroups are not pathogenic or belong to other pathogenic groups of E. coli. In addition, isolates falling outside of these serogroups are considered to be true EPEC. The definition of EPEC based on serotyping is inaccurate and should be replaced by methods that specifically detect the virulence properties of EPEC.

Virulence properties of Escherichia coli strains belonging to serogroups O26, O55, O111 and O128 isolated in the United Kingdom in 1991 from patients with diarrhoea

Some strains of Escherichia coli belonging to serogroups O26, O55, O111 or O128 produce Vero cytotoxin (VT). These serogroups are included in the range of enteropathogenic E. coli (EPEC) serogroups for which commercial antisera are available. In an attempt to obtain information on VT-producing strains other than those of serogroup O157, 122 strains belonging to these four serogroups and isolated in 1991 from patients with diarrhoea in the United Kingdom were tested for hybridization with VT probes. Only 18 of the 122 strains were VT-positive and these were O26 or O128. However 90 strains hybridized with the E. coli attaching and effacing (eae) probe (including 14 VT-positive strains) and 17 with the enteroaggregative E. coli (EAggEC) probe. For 78 eae-positive and 9 EAggEC-positive strains, tissue culture tests correlated with the probe results as the strains gave, respectively, either localized adhesion and a positive fluorescent-actin staining test or a characteristic aggregative attachment. A total of 111 of the 122 strains belonging to serogroups O26, O55, O111 or O128 possessed properties that may be associated with the ability to cause human diarrhoeal disease, and similar studies are needed on strains from the other classical EPEC serogroups.

Conventional screening for enteropathogenic Escherichia coli in the UK. Is it appropriate or necessary?

Enteropathogenic Escherichia coli (EPEC) is a well-recognized cause of infantile diarrhoea in the developing countries. In the developed countries, however, the incidence of EPEC associated outbreaks has dramatically declined. The last major outbreak in the UK was reported in 1980. This paper reviews the recent advances in the field of pathogenesis of diarrhoea caused by EPEC and questions the need to screen routinely for EPEC by conventional serological methods used in clinical microbiology laboratories in the UK.

Escherichia coli O128 strains from infants with diarrhea commonly show localized adhesion and positivity in the fluorescent-actin staining test but do not hybridize with an enteropathogenic E. coli adherence factor probe

Twenty-nine strains of Escherichia coli O128 isolated from infants with diarrhea that did not produce heat-stable enterotoxin, heat-labile enterotoxins, or Vero cytotoxin showed localized attachment to HEp-2 cells (LA). Only four strains hybridized with the enteropathogenic E. coli adherence factor (EAF) probe. One of the 25 LA+ EAF- strains attached to 72% of cells, while a plasmid-negative variant attached to 0.5% of cells. LA+ EAF- and LA+ EAF+ strains gave a positive fluorescent-actin staining test that correlates with the ability to cause attaching and effacing lesions in the intestine. The use of the EAF probe alone to detect LA+ strains is inadequate for epidemiological studies.