Extraintestinal Virulence Genes Research Articles

Shiga Toxin-Producing Escherichia coli Strains from Romania: A Whole Genome-Based Description.

The zoonotic Shiga toxin-producing Escherichia coli (STEC) group is unanimously regarded as exceptionally hazardous for humans. This study aimed to provide a genomic perspective on the STEC recovered sporadically from humans and have a foundation of internationally comparable data. Fifty clinical STEC isolates, representing the culture-confirmed infections reported by the STEC Reference Laboratory between 2016 and 2023, were subjected to whole-genome sequencing (WGS) analysis and sequences were interpreted using both commercial and public free bioinformatics tools. The WGS analysis revealed a genetically diverse population of STEC dominated by non-O157 serogroups commonly reported in human STEC infections in the European Union. The O26:H11 strains of ST21 lineage played a major role in the clinical disease resulting in hospitalisation and cases of paediatric HUS in Romania surpassing the O157:H7 strains. The latter were all clade 7 and mostly ST1804. Notably, among the Romanian isolates was a stx2a-harbouring cryptic clade I strain associated with a HUS case, stx2f- and stx2e-positive strains, and hybrid strains displaying a mixture of intestinal and extraintestinal virulence genes were found. As a clearer picture emerges of the STEC strains responsible for infections in Romania, further surveillance efforts are needed to uncover their prevalence, sources, and reservoirs.

Pathogenome comparison and global phylogeny of Escherichia coli ST1485 strains

Escherichia coli ST1485 strains belong to the clinically important phylogroup F and have disseminated worldwide in humans, animals, and the environment. Here, we elucidated the pathogenome of a global collection of E. coli ST1485 isolates from diverse sources retrieved from public databases and a high-quality sequenced complete genome of colistin-resistant E. coli strain CFSAN061771 isolated from raw milk cheese which designated as a reference strain. CFSAN061771 belongs to O83:H42-ST1485 pathotype and carries a conjugative ColV plasmid, pCFSAN061771_01, combining extraintestinal virulence genes (ompt, sitA, iroN, etsC, traT, cvaC, hylF, iss, tsh, mchf, iucC, iutA) with a multidrug resistance island (blaTEM-1, aph(6)-Id, aph(3″)-Ib, sul2, dfrA14). Comparative genomic analysis revealed a high frequency of pCFSAN061771_01-like plasmids in E. coli ST1485. A notable evolutionary genetic event in E. coli ST1485 strains is the acquisition of a pCFSAN061771_02-like plasmid, which confers resistance to several antimicrobials, tellurium, and quaternary ammonium compounds. The identical virulence and antibiotic resistance profiles identified in some human and animal strains are worrisome. This is the first study to emphasize the significance of E. coli ST1485 as a global high-risk virulent and multidrug-resistant clone with zoonotic potential.

Prevalence and characteristics of multidrug-resistant Escherichia coli sequence type ST131 at two academic centers in Boston and Minneapolis, USA

Escherichia coli sequence type (ST) ST131, with its emergent resistance-associated H30Rx, H30R1, and C1-M27 clonal subsets, accounts for the greatest share of extraintestinal E. coli infections and most extended-spectrum β-lactamase (ESBL)-producing E. coli. We characterized and compared consecutive E. coli urine isolates from two geographically distinct medical centers in Minneapolis, Minnesota (n=172) and Boston, Massachusetts (n=143) for ESBL phenotype, CTX-M-type ESBL genes, phylogenetic groups, selected ST131 subclones, and 40 extraintestinal virulence genes. Whereas the Boston vs. Minneapolis isolates had a similar prevalence of phylogenetic groups (mainly B2: 79% vs 73%), ST131 (34% vs 28%), H30 (28% vs 21%), and H30Rx (6% vs 5%), the emerging C1-M27 subclone occurred uniquely among Boston (6%) isolates. ESBL production was more prevalent among Boston isolates (15% vs 8%) and among ST131 isolates. Identified ESBL genes included blaCTX-M-27 (Boston only) and blaCTX-M-15. Ciprofloxacin resistance was ST131-associated and similarly prevalent across centers. Boston isolates had higher virulence gene scores. Despite numerous similarities to Minneapolis isolates, Boston ST131 isolates demonstrated more prevalent ESBL production, higher virulence gene scores, and, uniquely, the C1-M27 subclone and blaCTX-M-27. Broader surveillance is needed to define the prevalence of ST131's globally successful C1-M27 subclone across the U.S.

Epidemiology and genomic analysis of Shiga toxin-producing Escherichia coli clonal complex 165 in the UK

IntroductionShiga toxin-producing Escherichia coli (STEC) is a zoonotic, foodborne gastrointestinal pathogen that has the potential to cause severe clinical outcomes, including haemolytic uraemic syndrome (HUS). STEC-HUS is the leading cause of renal failure in children and can be fatal. Over the last decade, STEC clonal complex 165 (CC165) has emerged as a cause of STEC-HUS.Gap statementThere is a need to understand the pathogenicity and prevalence of this emerging STEC clonal complex in the UK, to facilitate early diagnosis, improve clinical management, and prevent and control outbreaks.AimThe aim of this study was to characterize CC165 through identification of virulence factors (VFs) and antimicrobial resistance (AMR) determinants in the genome and to integrate the genome data with the available epidemiological data to better understand the incidence and pathogenicity of this clonal complex in the UK.MethodologyAll isolates belonging to CC165 in the archives at the UK public health agencies were sequenced and serotyped, and the virulence gene and AMR profiles were derived from the genome using PHE bioinformatics pipelines and the Centre for Genomic Epidemiology virulence database.ResultsThere were 48 CC165 isolates, of which 43 were STEC, four were enteropathogenic E. coli (EPEC) and one E. coli . STEC serotypes were predominately O80:H2 (n=28), and other serotypes included O45:H2 (n=9), O55:H9 (n=4), O132:H2 (n=1) and O180:H2 (n=1). All but one STEC isolate had Shiga toxin (stx) subtype stx2a or stx2d and 47/48 isolates had the eae gene encoding intimin involved in the intimate attachment of the bacteria to the human gut mucosa. We detected extra-intestinal virulence genes including those associated with iron acquisition (iro) and serum resistance (iss), indicating that this pathogen has the potential to translocate to extra-intestinal sites. Unlike other STEC clonal complexes, a high proportion of isolates (93%, 40/43) were multidrug-resistant, including resistance to aminoglycosides, beta-lactams, chloramphenicol, sulphonamides, tetracyclines and trimethoprim.ConclusionThe clinical significance of this clonal complex should not be underestimated. Exhibiting high levels of AMR and a combination of STEC and extra-intestinal pathogenic E. coli (ExPEC) virulence profiles, this clonal complex is an emerging threat to public health.

The E phylogroup of Escherichia coli is highly diverse and mimics the whole E. coli species population structure.

To get a global picture of the population structure of the Escherichia coli phylogroup E, encompassing the O157:H7 EHEC lineage, we analysed the whole genome of 144 strains isolated from various continents, hosts and lifestyles and representative of the phylogroup diversity. The strains possess 4331 to 5440 genes with a core genome of 2771 genes and a pangenome of 33 722 genes. The distribution of these genes among the strains shows an asymmetric U-shaped distribution. E phylogenetic strains have the largest genomes of the species, partly explained by the presence of mobile genetic elements. Sixty-eight lineages were delineated, some of them exhibiting extra-intestinal virulence genes and being virulent in the mouse sepsis model. Except for the EHEC lineages and the reference EPEC, EIEC and ETEC strains, very few strains possess intestinal virulence genes. Most of the strains were devoid of acquired resistance genes, but eight strains possessed extended-spectrum beta-lactamase genes. Human strains belong to specific lineages, some of them being virulent and antibiotic-resistant [sequence type complexes (STcs) 350 and 2064]. The E phylogroup mimics all the features of the species as a whole, a phenomenon already observed at the STc level, arguing for a fractal population structure of E. coli.

Molecular Epidemiology of Multidrug-resistant Escherichia coli from Urinary Tract Infections

Objectives: The purpose of this study was to investigate the phylogenetic groups, antibiotic resistance, antibiotic resistance genes (ARGs), integrons, extraintestinal virulence genes and genetic diversity of Escherichia coli isolates from human urinary tract infection. Methods: A total of 100 E. coli isolates were collected from patients with urinary tract infections in Kerala, South India. Antibiotic susceptibility testing of all E. coli isolates against different antibiotics was determined by the disc diffusion method. Phylogenetic groups, extraintestinal virulence genes, ARGs, and integrons were detected by PCR. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) was used to check the genetic relatedness among E. coli isolates. Results: E. coli isolates have mainly belonged to phylogenetic group B2. Resistance to ampicillin was most frequent among the E. coli isolates followed by resistance to cefoxitin, cefpodoxime, nalidixic acid, trimethoprim, and co-trimoxazole. Among E. coli isolates, 96% were multidrug-resistant (MDR), and 86% and 32% harbored ARGs and integrase 1 (int1) respectively. Seventy-nine percent of the isolates were extraintestinal pathogenic E. coli (ExPEC), and 86% of them (n = 68) harbored ARGs. One extensively drug-resistant (XDR) ExPEC was obtained in this study. The present study revealed a significant association between the presence of virulence genes and antibiotic resistance. A high degree of genetic diversity was observed among the ARGs-harboring E. coli isolates. Conclusion: Understanding the association between extraintestinal virulence genes and antibiotic resistance genes would result in the proper treatment of urinary tract infections. J Microbiol Infect Dis 2021; 11(2):66-73.

Prevalence of colistin-resistant Escherichia coli harbouring mcr-1 in raw beef and ready-to-eat beef products in Egypt

The emergence of antibiotic-resistant bacteria in food, mainly contaminated meat and its products, and their transfer to humans is of great concern. To evaluate the potential risk of such contamination in Egypt, we isolated Escherichia coli from 78% (51/65) of raw beef and 53% (24/45) of ready-to-eat beef products. Of the 210 E. coli isolates detected, 8 (3.8%) harboured mcr-1 gene and were resistant to colistin, whereas 5 (2.4%) were positive for the blaCTX-M-28 gene and were resistant to cefotaxime. Among the colistin-resistant isolates, three had both mcr-1 and extended-spectrum beta-lactamase (ESBL) genes, constituting a great public health concern. The sequence types of all these mcr and/or ESBL-positive isolates were variable, suggesting that colistin and/or cephalosporin resistance spread through the mediation of plasmids harbouring mcr-1 or ESBL genes in Egyptian beef. In addition, various extraintestinal virulence genes were observed in some isolates. Colistin and cephalosporins are frequently used for livestock in Egypt; hence the present results suggest colistin and cephalosporin-resistant pathogenic E. coli are transferred from food animals to humans via meat and meat-derived products. Therefore, the rational use of antimicrobials and the appropriate safety measures in food production are needed in Egypt as well as in other developing countries.

Extended Phylogeny and Extraintestinal Virulence Potential of Commensal Escherichia coli from Piglets and Sows.

Commensal Escherichia coli, naturally occurring in the intestinal tract, can be the origin of extraintestinal pathogenic E. coli (ExPEC) strains. ExPEC causes high mortality and significant economic losses in the swine industry in several countries and poses a serious threat to public health worldwide. The aim of this study was to analyze the extended phylogenetic structure and extraintestinal virulence potential in two groups of commensal E. coli isolates from post-weaning piglets and sows. The phylogenetic assignment to eight groups was determined using the revised Clermont phylogenetic typing method in quadruplex PCR. Identification of extraintestinal virulence genes (VGs) and adhesin operon genes was performed using multiplex or simplex PCR. The revised phylogenetic assignment allowed us to distinguish E. coli with significantly higher (groups C and F) or lower (group E) virulence potential in isolates from piglets. The majority of the tested VGs occurred more frequently in isolates from piglets than from sows, with statistically significant differences for seven genes: fimH, papAH, iutA, iroN, ompT, traT, and iss. Complete operons for type I and P fimbriae significantly prevailed among E. coli from piglets. This study provides insight into the extended phylogenetic structure of porcine commensal E. coli and showed that these strains, particularly from piglets, constitute a considerable reservoir of extraintestinal VGs and may increase the potential risk of extraintestinal infections.

Screening of tropical estuarine water in south-west coast of India reveals emergence of ARGs-harboring hypervirulent Escherichia coli of global significance.

The goal of this study was to investigate the involvement of a tropical Indian estuary in the emergence of antibiotic resistance genes (ARGs)-harboring hypervirulent E. coli of global significance. A total of 300 E. coli isolates was tested for antibiotic susceptibility to β-lactams, aminoglycosides, chloramphenicol, quinolones, sulphonamides, tetracyclines, and trimethoprim. The E. coli isolates were screened for the presence of antibiotic resistance genes (blaTEM, blaCTX-M, tetA, tetB, sul1, sul2, strA, aphA2, catI, dhfr1, and dhfr7), integrase (int1, int2, and int3), Shiga toxin genes (stx1 and stx2) and extraintestinal virulence genes (papAH, papC, sfa/focDE, kpsMT II, and iutA). The highest prevalence of antibiotic resistance was observed for ampicillin, followed by tetracycline, and nalidixic acid. Among E. coli isolates, 64% were resistant to at least one of the 15 antibiotics tested, and approximately 40% were multiple antibiotic-resistant (MAR). More than 40% (n = 122) of E. coli isolates had ARGs. Integrase 1 (int1) was found in 7.6% of E. coli isolates. Among E. coli isolates, 16.3% (n = 49) were extraintestinal pathogenic E. coli (ExPEC), and approximately 34.6% (n = 17) of ExPEC had ARGs. A hypervirulent ARGs-harboring STEC was isolated. The prevalence of Shiga toxin-producing E. coli (STEC) was low (n = 1). The prevalence of ARGs-harboring pathogenic E. coli isolates was higher in stations close to the City (urban area), than that of other stations. ERIC-PCR (enterobacterial repetitive intergenic consensus sequence polymerase chain reaction) analysis revealed a high degree of genetic diversity among the ARGs-harboring E. coli isolates. The results demonstrate a high prevalence of ARGs-harboring E. coli in estuarine water and confirm the need for a better wastewater treatment facility and proper control measures to reduce the discharge of sewage and wastewater into the aquatic environments.

Genetic characterization of Shiga toxin producing Escherichia coli belonging to the emerging hybrid pathotype O80:H2 isolated from humans 2010–2017 in Switzerland

Shiga toxin-producing E. coli (STEC) O80:H2 is an uncommon hybrid pathotype that has recently emerged in France. We analysed 18 STEC O80:H2 isolated from humans in Switzerland during 2010–2017. All isolates carried stx2a or stx2d, the rare eae variant eae-ξ and at least seven virulence genes associated with pS88, a plasmid that is found in extraintestinal pathogenic E. coli (ExPEC). Whole genome sequencing (WGS) identified additional chromosomal extraintestinal virulence genes encoding for type 1 fimbria (fimA, fimC and fimH), aerobactin (iuc/iutA) and afimbrial adhesins (afaA/C/D/E-VIII). Core genome multi-locus sequence typing (cgMLST) detected two closely related but distinct subclusters with different stx2 and iuc/iutA genotypes. All isolates were multidrug resistant (MDR), but susceptible to third generation cephalosporins and azithromycin. STEC/ExPEC hybrid pathotypes such as STEC O80:H2 represent a therapeutical challenge in the event of extraintestinal infection.

Comparative virulotyping of extended-spectrum cephalosporin-resistant E. coli isolated from broilers, humans on broiler farms and in the general population and UTI patients

During the last decade extended-spectrum cephalosporin (ESC)-resistant Escherichia coli from food-producing animals, especially from broilers, have become a major public health concern because of the potential transmission of these resistant bacteria or their plasmid-encoded resistance genes to humans. The objective of this study was to compare ESC-resistant E. coli isolates from broilers (n=149), humans in contact with these broilers (n=44), humans in the general population (n=63), and patients with a urinary tract infection (UTI) (n=10) with respect to virulence determinants, phylogenetic groups and extended-spectrum β-lactamase (ESBL)/plasmidic-AmpC (pAmpC) genes. The most prevalent ESBL/pAmpC genes among isolates from broilers and individuals on broiler farms were blaCTX-M-1, blaCMY-2 and blaSHV-12. In isolates from humans in the general population blaCTX-M-1, blaCTX-M-14 and blaCTX-M-15 were found most frequently, whereas in UTI isolates blaCTX-M-15 predominated. The marker for enteroaggregative E. coli, aggR, was only identified in a broiler and human isolates from the general population. The extraintestinal virulence genes afa and hlyD were exclusively present in human isolates in the general population and UTI isolates. Multivariate analysis, based on ESBL/pAmpC resistance genes, virulence profiles and phylogenetic groups, revealed that most UTI isolates formed a clearly distinct group. Isolates from broilers and humans associated with broiler farms clustered together. In contrast, isolates from the general population showed some overlap with the former two groups but primarily formed a separate group. These results indicate than transmission occurs between broilers and humans on broiler farms, but also indicate that the role of broilers as a source of foodborne transmission of ESC-resistant E. coli to the general population and subsequently causative agents of human urinary tract infections is likely relatively small.

Age as a Factor Influencing Diversity of Commensal E. coli Microflora in Pigs

Commensal, intestinal E. coli microflora plays a role in maintenance of intestinal balance of the host, is responsible for defending against pathogenic E. coli. This study encompasses the analysis of BOX-PCR fingerprinting patterns, phylogenetic grouping and virulence genes prevalence among commensal E. coli isolates derived from healthy pigs. Altogether, 274 unique E. coli isolates were identified, 110 from weaned piglets (Piglets I and Piglets II) and 164 from adult sows (Sows I and Sows II). BOX-PCR analysis distinguished isolates from pigs in different age and indicated that during maturation the changes in E. coli microflora occurred. Phylogenetic grouping revealed significant differences between distribution of four phylogenetic groups among isolates derived from piglets and sows. In phylogenetic structure of isolates from the piglets group B1 prevailed significantly, while among isolates derived from the sows the majority of them were classified into phylogenetic group A. The identification of 17 virulence factors in E. coli isolates derived from healthy pigs was performed. Three of 13 intestinal (escV, ehxA, estII) and four extra-intestinal virulence genes (VGs) (hlyA, fimH, papA, sfaS) were detected in the porcine isolates. The percentage of VGs positive isolates among piglets is higher than among sows, moreover, the VGs occurring in E. coli isolates from piglets revealed greater diversity than that detected among isolates from sows.

Occurrence of Intestinal and Extraintestinal Virulence Genes in Escherichia coli Isolates from Rainwater Tanks in Southeast Queensland, Australia

In this study, 200 Escherichia coli isolates from 22 rainwater tank samples in Southeast Queensland, Australia, were tested for the presence of 20 virulence genes (VGs) associated with intestinal and extraintestinal pathotypes. In addition, E. coli isolates were also classified into phylogenetic groups based on the detection of the chuA, yjaA, and TSPE4.C2 genes. Of the 22 rainwater tanks, 8 (36%) and 5 (23%) were positive for the eaeA (belonging to enteropathogenic E. coli [EPEC] and Shiga-toxigenic E. coli [STEC]) and ST1 (belonging to enterotoxigenic E. coli [ETEC]) genes, respectively. VGs (cdtB, cvaC, ibeA, kpsMT allele III, PAI, papAH, and traT) belonging to extraintestinal pathogenic E. coli (ExPEC) were detected in 15 (68%) of the 22 rainwater tanks. Of the 22 samples, 17 (77%) and 11 (50%) contained E. coli belonging to phylogenetic groups A and B1, respectively. Similarly, 10 (45%) and 16 (72%) contained E. coli belonging to phylogenetic groups B2 and D, respectively. Of the 96 of the 200 strains from 22 tanks that were VG positive, 40 (42%) were carrying a single VG, 36 (37.5%) were carrying two VGs, 17 (18%) were carrying three VGs, and 3 (3%) had four or more VGs. This study reports the presence of multiple VGs in E. coli strains belonging to the STEC, EPEC, ETEC, and ExPEC pathotypes in rainwater tanks. The public health risks associated with potentially clinically significant E. coli in rainwater tanks should be assessed, as the water is used for drinking and other, nonpotable purposes. It is recommended that rainwater be disinfected using effective treatment procedures such as filtration, UV disinfection, or simply boiling prior to drinking.

Colonisation dynamics and virulence of two clonal groups of multidrug-resistant Escherichia coli isolated from dogs

The study established the virulence potential of multidrug-resistant Escherichia coli (MDREC) isolates from nosocomial infections in hospitalised dogs. The isolates were resistant to fluoroquinolones, belonged to two distinct clonal groups (CG1 and CG2) and contained a plasmid-mediated AmpC (CMY-7) β-lactamase. CG1 isolates ( n = 14) possessed two of 36 assayed extraintestinal virulence genes ( iutA and traT) and belonged to phylogenetic group A, whereas CG2 isolates ( n = 19) contained four such genes ( iutA, ibeA, fimH and kpsMT K5) and belonged to group D. In a mouse gastrointestinal tract colonisation model, colonisation by index CG1 strain C1 was transient, in contrast to the index CG2 strain C2b, which persisted up to 40 days post-inoculation. In a mouse subcutaneous challenge model, both strains were less virulent than archetypal group B2 extraintestinal pathogenic E. coli (ExPEC) strain CFT073; strain C1 caused no systemic signs and strain C2b was lethal to only one of six mice. In a mouse urinary tract infection model, strain C2b colonised the mouse bladder over 2 logs higher compared to strain C1. Whilst both groups of canine MDREC appear less virulent than a reference human ExPEC strain, CG2 strains have greater capacity for colonisation and virulence.

Identification of forces shaping the commensal Escherichia coli genetic structure by comparing animal and human isolates

To identify forces shaping the Escherichia coli intraspecies ecological structure, we have characterized in terms of phylogenetic group (A, B1, D and B2) belonging, presence/absence of extraintestinal virulence genes (pap, sfa, hly and aer) and intra-host phylotype diversity a collection of 1898 commensal isolates originating from 387 animals (birds and mammals) sampled in the 1980s and the 2000s. These data have been compared with 760 human commensal isolates, sampled from 152 healthy subjects in the 2000s, and analysed with the same approach. The prevalence of the E. coli phylogenetic groups in birds, non-human mammals and humans is clearly different with a predominance of D/B1, A/B1 and A/B2 strains respectively. A major force shaping the ecological structure is the environment with a strong effect of domestication and the year of sampling followed by the climate. Host characteristics, as the diet and body mass, also influence the ecological structure. Human microbiota are characterized by a higher prevalence of virulence genes and a lower intra-host diversity than the non-human mammal ones. This work identifies for the first time a group of strains specific to the animals, the B1 phylogenetic group strains exhibiting the hly gene. In conclusion, a complex network of factors seems to shape the ecological structure of commensal E. coli, with anthropogenic factors playing a major role and perturbing natural niche equilibrium.

Host-Pathogen Relationships among Escherichia coli Isolates Recovered from Men with Febrile Urinary Tract Infection

Host-pathogen relationships in men with febrile urinary tract infection (FUTI) are poorly understood. Phylogenetic background, extended virulence genotypes, and serotypes were determined for 70 Escherichia coli isolates recovered from urine samples obtained from men with FUTI for comparison with available data for 70 E. coli rectal isolates recovered from uninfected men. Bacterial traits were assessed in relation to underlying host characteristics (age, compromise status, and history of urinary tract infection) and acute manifestations (bacteremia, flank pain, and serum prostate-specific antigen [PSA] level). Compared with rectal isolates, FUTI isolates exhibited a significantly higher prevalence of virulence-associated phylogenetic groups, serotypes, and extraintestinal virulence genes. The latter included traditional prostatitis-associated traits (e.g., hemolysin and cytotoxic necrotizing factor), as well as unconventional traits, such as outer membrane protease T. These bacterial traits occurred largely independent of host age, urological compromise status, urinary tract infection history, and acute manifestations. However, certain traits were less prevalent in association with use of urinary tract instrumentation and significantly predicted elevated PSA levels. Considerable virulence capability may be required for an E. coli strain to cause FUTI in men, regardless of whether most compromising conditions are present. Bacterial traits that promote prostatic invasion may be relevant for the pathogenesis of FUTI, even among men without classic manifestations of acute prostatitis.

Characterization of Escherichia coli strains isolated from environmental water habitats and from stool samples of healthy volunteers

This study was undertaken to determine the frequency of pathogenic Escherichia coli strains among wild-type E. coli strain isolates from the microbial flora of healthy volunteers and from natural residential water habitats of a defined geographic area. In total, 131 stool and 95 water isolates as well as 14 E. coli K12 strains were examined for DNA sequences specific for 20 different genes encoding E. coli pathogenicity factors, including adherence factors, toxins, invasins, capsules and iron uptake systems. The expression of the corresponding pathogenicity factors was also investigated. No pathogenicity factors were found to be present in the tested E. coli K12 strains. In contrast, 41.0% of the water samples and 63.4% of the stool samples contained pathogenicity factors specific for extraintestinal E. coli pathogens. While no virulence determinants specific for intestinal E. coli pathogens were found among the investigated environmental water isolates, 4.5% of the stool samples contained either only intestinal or both intestinal and extraintestinal virulence genes. Both the prevalence of the virulence genes and the expression of the corresponding pathogenicity factors were, in general, higher in stool than in water samples. These findings might indicate the prevalence of different clonal types and/or differential regulation of pathogenicity factor expression in diverse ecological niches.