Biological and Physicochemical Wastewater Treatment Processes Reduce the Prevalence of Virulent Escherichia coli

ABSTRACTEffluents discharged from wastewater treatment plants are possible sources of pathogenic bacteria, includingEscherichia coli, in the freshwater environment, and determining the possible selection of pathogens is important. This study evaluated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of potentially virulentE. coli. A total of 719E. coliisolates collected from four municipal plants in Québec before and after treatment were characterized by using a customized DNA microarray to determine the impact of treatment processes on the frequency of specific pathotypes and virulence genes. The percentages of potentially pathogenicE. coliisolates in the plant influents varied between 26 and 51%, and in the effluents, the percentages were 14 to 31%, for a reduction observed at all plants ranging between 14 and 45%. Pathotypes associated with extraintestinal pathogenicE. coli(ExPEC) were the most abundant at three of the four plants and represented 24% of all isolates, while intestinal pathogenicE. colipathotypes (IPEC) represented 10% of the isolates. At the plant where ExPEC isolates were not the most abundant, a large number of isolates were classified as both ExPEC and IPEC; overall, 6% of the isolates were classified in both groups, with the majority being from the same plant. The reduction of the proportion of pathogenicE. colicould not be explained by the preferential loss of one virulence gene or one type of virulence factor; however, the quinolone resistance gene (qnrS) appears to enhance the loss of virulence genes, suggesting a mechanism involving the loss of pathogenicity islands.

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Retention in Treated Wastewater Affects Survival and Deposition of Staphylococcus aureus and Escherichia coli in Sand Columns

Applied and Environmental Microbiology ◽

10.1128/aem.03740-14 ◽

2015 ◽

Vol 81 (6) ◽

pp. 2199-2205 ◽

Cited By ~ 5

Author(s):

Jiuyi Li ◽

Xiaokang Zhao ◽

Xiujun Tian ◽

Jin Li ◽

Jelmer Sjollema ◽

...

Keyword(s):

Escherichia Coli ◽

Staphylococcus Aureus ◽

Wastewater Treatment ◽

Pathogenic Bacteria ◽

Treated Wastewater ◽

Growth Media ◽

Surface Charges ◽

Content Type ◽

Treatment Facilities ◽

The Impact

ABSTRACTThe fate and transport of pathogenic bacteria from wastewater treatment facilities in the Earth's subsurface have attracted extensive concern over recent decades, while the impact of treated-wastewater chemistry on bacterial viability and transport behavior remains unclear. The influence of retention time in effluent from a full-scale municipal wastewater treatment plant on the survival and deposition ofStaphylococcus aureusandEscherichia colistrains in sand columns was investigated in this paper. In comparison to the bacteria cultivated in nutrient-rich growth media, retention in treated wastewater significantly reduced the viability of all strains. Bacterial surface properties, e.g., zeta potential, hydrophobicity, and surface charges, varied dramatically in treated wastewater, though no universal trend was found for different strains. Retention in treated wastewater effluent resulted in changes in bacterial deposition in sand columns. Longer retention periods in treated wastewater decreased bacterial deposition rates for the strains evaluated and elevated the transport potential in sand columns. We suggest that the wastewater quality should be taken into account in estimating the fate of pathogenic bacteria discharged from wastewater treatment facilities and the risks they pose in the aquatic environment.

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Clinical and Molecular Correlates of Escherichia coli Bloodstream Infection from Two Geographically Diverse Centers in Rochester, Minnesota, and Singapore

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00937-18 ◽

2018 ◽

Vol 62 (10) ◽

Cited By ~ 5

Author(s):

Shehara M. Mendis ◽

Shawn Vasoo ◽

Brian D. Johnston ◽

Stephen B. Porter ◽

Scott A. Cunningham ◽

...

Keyword(s):

Escherichia Coli ◽

Odds Ratio ◽

Virulence Gene ◽

Fluoroquinolone Resistance ◽

Content Type ◽

E Coli ◽

Gene Profiles ◽

Clonal Distribution ◽

To Receive ◽

Community Onset

ABSTRACT Escherichia coli bacteremia is caused mainly by sequence type complex 131 (STc131) and two clades within its fluoroquinolone-resistance-associated H30 subclone, H30R1 and H30Rx. We examined clinical and molecular correlates of E. coli bacteremia in two geographically distinct centers. We retrospectively studied 251 unique E. coli bloodstream isolates from 246 patients (48 from the Mayo Clinic, Rochester, MN [MN], and 198 from Tan Tock Seng Hospital, Singapore [SG]), from October 2013 through March 2014. Isolates underwent PCR for phylogroup, STc, blaCTX-M type, and virulence gene profiles, and medical records were reviewed. Although STc131 accounted for 25 to 27% of all E. coli bacteremia isolates at each site, its extended-spectrum-β-lactamase (ESBL)-associated H30Rx clade was more prominent in SG than in MN (15% versus 4%; P = 0.04). In SG only, patients with STc131 (versus other E. coli STc isolates) were more likely to receive inactive initial antibiotics (odds ratio, 2.8; P = 0.005); this was true specifically for patients with H30Rx (odds ratio, 7.0; P = 0.005). H30Rx comprised 16% of community-onset bacteremia episodes in SG but none in MN. In SG, virulence scores were higher for H30Rx than for H30R1, non-H30 STc131, and non-STc131 isolates (P < 0.02 for all comparisons). At neither site did mortality differ by clonal status. The ESBL-associated H30Rx clade was more prevalent and more often of community onset in SG, where it predicted inactive empirical treatment. The clonal distribution varies geographically and has potentially important clinical implications. Rapid susceptibility testing and clonal diagnostics for H30/H30Rx might facilitate earlier prescribing of active therapy.

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Impact of Extended-Spectrum β-Lactamase Production on Treatment Outcomes of Acute Pyelonephritis Caused by Escherichia coli in Patients without Health Care-Associated Risk Factors

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.04821-14 ◽

2015 ◽

Vol 59 (4) ◽

pp. 1962-1968 ◽

Cited By ~ 13

Author(s):

Sun Hee Park ◽

Su-Mi Choi ◽

Dong-Gun Lee ◽

Sung-Yeon Cho ◽

Hyo-Jin Lee ◽

...

Keyword(s):

Risk Factors ◽

Escherichia Coli ◽

Health Care ◽

Treatment Outcomes ◽

Acute Pyelonephritis ◽

Esbl Production ◽

Content Type ◽

E Coli ◽

Extended Spectrum ◽

The Impact

ABSTRACTExtended-spectrum β-lactamase-producingEscherichia coli(ESBL-EC) is increasingly identified as a cause of acute pyelonephritis (APN) among patients without recent health care contact, i.e., community-associated APN. This case-control study compared 75 cases of community-associated ESBL-EC APN (CA-ESBL) to 225 controls of community-associated non-ESBL-EC APN (CA-non-ESBL) to identify the risk factors for ESBL-EC acquisition and investigate the impact of ESBL on the treatment outcomes of community-associated APN (CA-APN) caused byE. coliat a Korean hospital during 2007 to 2013. The baseline characteristics were similar between the cases and controls; the risk factors for ESBL-EC were age (>55 years), antibiotic use within the previous year, and diabetes with recurrent APN. The severity of illness did not differ between CA-ESBL and CA-non-ESBL (Acute Physiology and Chronic Health Evaluation [APACHE] II scores [mean ± standard deviation], 7.7 ± 5.9 versus 6.4 ± 5.3;P= 0.071). The proportions of clinical (odds ratio [OR], 1.76; 95% confidence interval [CI], 0.57 to 5.38;P= 0.323) and microbiological (OR, 1.16; 95% CI, 0.51 to 2.65;P= 0.730) cures were similar, although the CA-ESBL APN patients were less likely to receive appropriate antibiotics within 48 h. A multivariable Cox proportional hazards analysis of the prognostic factors for CA-APN caused byE. colishowed that ESBL production was not a significant factor for clinical (hazard ratio [HR], 0.39; 95% CI, 0.12 to 1.30;P= 0.126) or microbiological (HR, 0.49; 95% CI, 0.21 to 1.12;P= 0.091) failure. The estimates did not change after incorporating weights calculated using propensity scores for acquiring ESBL-EC. Therefore, ESBL production did not negatively affect treatment outcomes among patients with community-associatedE. coliAPN.

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Molecular characterisation of antimicrobial resistance and virulence genes in Escherichia coli strains isolated from diarrhoeic and healthy rabbits in Tunisia

World Rabbit Science ◽

10.4995/wrs.2020.10879 ◽

2020 ◽

Vol 28 (2) ◽

pp. 81

Author(s):

Raouia Ben Rhouma ◽

Ahlem Jouini ◽

Amira Klibi ◽

Safa Hamrouni ◽

Aziza Boubaker ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Virulence Genes ◽

Antimicrobial Agents ◽

Antibiotic Resistance Genes ◽

Virulence Gene ◽

Diffusion Method ◽

Class 1 Integron ◽

E Coli ◽

Class 1

The purpose of this study was to identify Escherichia coli isolates in diarrhoeic and healthy rabbits in Tunisia and characterise their virulence and antibiotic resistance genes. In the 2014-2015 period, 60 faecal samples from diarrhoeic and healthy rabbits were collected from different breeding farms in Tunisia. Susceptibility to 14 antimicrobial agents was tested by disc diffusion method and the mechanisms of gene resistance were evaluated using polymerase chain reaction and sequencing methods. Forty E. coli isolates were recovered in selective media. High frequency of resistance to tetracycline (95%) was detected, followed by different levels of resistance to sulphonamide (72.5%), streptomycin (62.5%), trimethoprim-sulfamethoxazole (60%), nalidixic acid (32.5%), ampicillin (37.5%) and ticarcillin (35%). E. coli strains were susceptible to cefotaxime, ceftazidime and imipenem. Different variants of blaTEM, tet, sul genes were detected in most of the strains resistant to ampicillin, tetracycline and sulphonamide, respectively. The presence of class 1 integron was studied in 29 sulphonamide-resistant E. coli strains from which 15 harboured class 1 integron with four different arrangements of gene cassettes, dfrA17+aadA5 (n=9), dfrA1 + aadA1 (n=4), dfrA12 + addA2 (n=1), dfrA12+orf+addA2 (n=1). The qnrB gene was detected in six strains out of 13 quinolone-resistant E. coli strains. Seventeen E. coli isolates from diarrhoeic rabbits harboured the enteropathogenic eae genes associated with different virulence genes tested (fimA, cnf1, aer), and affiliated to B2 (n=8) and D (n=9) phylogroups. Isolated E. coli strains from healthy rabbit were harbouring fim A and/or cnf1 genes and affiliated to A and B1 phylogroups. This study showed that E. coli strains from the intestinal tract of rabbits are resistant to the widely prescribed antibiotics in medicine. Therefore, they constitute a reservoir of antimicrobial-resistant genes, which may play a significant role in the spread of antimicrobial resistance. In addition, the eae virulence gene seemed to be implicated in diarrhoea in breeder rabbits in Tunisia.

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d-Serine induces distinct transcriptomes in diverse Escherichia coli pathotypes

Microbiology ◽

10.1099/mic.0.001093 ◽

2021 ◽

Vol 167 (10) ◽

Author(s):

James P. R. Connolly ◽

Natasha C. A. Turner ◽

Jennifer C. Hallam ◽

Patricia T. Rimbi ◽

Tom Flett ◽

...

Keyword(s):

Escherichia Coli ◽

Type Species ◽

Pathogenic Bacteria ◽

Neonatal Meningitis ◽

Published Data ◽

Toxic Metabolite ◽

Transcriptional Responses ◽

Content Type ◽

E Coli ◽

Link Type

Appropriate interpretation of environmental signals facilitates niche specificity in pathogenic bacteria. However, the responses of niche-specific pathogens to common host signals are poorly understood. d-Serine (d-ser) is a toxic metabolite present in highly variable concentrations at different colonization sites within the human host that we previously found is capable of inducing changes in gene expression. In this study, we made the striking observation that the global transcriptional response of three Escherichia coli pathotypes – enterohaemorrhagic E. coli (EHEC), uropathogenic E. coli (UPEC) and neonatal meningitis-associated E. coli (NMEC) – to d-ser was highly distinct. In fact, we identified no single differentially expressed gene common to all three strains. We observed the induction of ribosome-associated genes in extraintestinal pathogens UPEC and NMEC only, and the induction of purine metabolism genes in gut-restricted EHEC, and UPEC indicating distinct transcriptional responses to a common signal. UPEC and NMEC encode dsdCXA – a genetic locus required for detoxification and hence normal growth in the presence of d-ser. Specific transcriptional responses were induced in strains accumulating d-ser (WT EHEC and UPEC/NMEC mutants lacking the d-ser-responsive transcriptional activator DsdC), corroborating the notion that d-ser is an unfavourable metabolite if not metabolized. Importantly, many of the UPEC-associated transcriptome alterations correlate with published data on the urinary transcriptome, supporting the hypothesis that d-ser sensing forms a key part of urinary niche adaptation in this pathotype. Collectively, our results demonstrate distinct pleiotropic responses to a common metabolite in diverse E. coli pathotypes, with important implications for niche selectivity.

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Subtilase Cytotoxin-Coding Genes in Verotoxin-Producing Escherichia coli Strains from Sheep and Goats Differ from Those from Cattle

Applied and Environmental Microbiology ◽

10.1128/aem.05604-11 ◽

2011 ◽

Vol 77 (23) ◽

pp. 8259-8264 ◽

Cited By ~ 11

Author(s):

José A. Orden ◽

Pilar Horcajo ◽

Ricardo de la Fuente ◽

José A. Ruiz-Santa-Quiteria ◽

Gustavo Domínguez-Bernal ◽

...

Keyword(s):

Escherichia Coli ◽

Human Disease ◽

Virulence Genes ◽

Small Ruminants ◽

Human Beings ◽

Content Type ◽

Sheep And Goats ◽

E Coli ◽

Healthy Cattle ◽

Subtilase Cytotoxin

ABSTRACTSubtilase cytotoxin (SubAB) from verotoxin (VT)-producingEscherichia coli(VTEC) strains was first described in the 98NK2 strain and has been associated with human disease. However, SubAB has recently been found in two VT-negativeE. colistrains (ED 591 and ED 32). SubAB is encoded by two closely linked, cotranscribed genes (subAandsubB). In this study, we investigated the presence ofsubABgenes in 52 VTEC strains isolated from cattle and 209 strains from small ruminants, using PCR. Most (91.9%) VTEC strains from sheep and goats and 25% of the strains from healthy cattle possessedsubABgenes. The presence ofsubABin a high percentage of the VTEC strains from small ruminants might increase the pathogenicity of these strains for human beings. Some differences in the results of PCRs and in the association with some virulence genes suggested the existence of different variants ofsubAB. We therefore sequenced thesubAgene in 12 strains and showed that thesubAgene in most of thesubAB-positive VTEC strains from cattle was almost identical (about 99%) to that in the 98NK2 strain, while thesubAgene in most of thesubAB-positive VTEC strains from small ruminants was almost identical to that in the ED 591 strain. We propose the termssubAB1to describe the SubAB-coding genes resembling that in the 98NK2 strain andsubAB2to describe those resembling that in the ED 591 strain.

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Impact of UV and Peracetic Acid Disinfection on the Prevalence of Virulence and Antimicrobial Resistance Genes in Uropathogenic Escherichia coli in Wastewater Effluents

Applied and Environmental Microbiology ◽

10.1128/aem.00418-14 ◽

2014 ◽

Vol 80 (12) ◽

pp. 3656-3666 ◽

Cited By ~ 24

Author(s):

Basanta Kumar Biswal ◽

Ramzi Khairallah ◽

Kareem Bibi ◽

Alberto Mazza ◽

Ronald Gehr ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Peracetic Acid ◽

Content Type ◽

E Coli ◽

Antimicrobial Resistance Genes ◽

Antimicrobial Resistance Gene ◽

Municipal Wastewaters ◽

The Impact

ABSTRACTWastewater discharges may increase the populations of pathogens, includingEscherichia coli, and of antimicrobial-resistant strains in receiving waters. This study investigated the impact of UV and peracetic acid (PAA) disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenicEscherichia coli(UPEC), the most abundantE. colipathotype in municipal wastewaters. Laboratory disinfection experiments were conducted on wastewater treated by physicochemical, activated sludge, or biofiltration processes; 1,766E. coliisolates were obtained for the evaluation. The target disinfection level was 200 CFU/100 ml, resulting in UV and PAA doses of 7 to 30 mJ/cm2and 0.9 to 2.0 mg/liter, respectively. The proportions of UPECs were reduced in all samples after disinfection, with an average reduction by UV of 55% (range, 22% to 80%) and by PAA of 52% (range, 11% to 100%). Analysis of urovirulence genes revealed that the decline in the UPEC populations was not associated with any particular virulence factor. A positive association was found between the occurrence of urovirulence and antimicrobial resistance genes (ARGs). However, the changes in the prevalence of ARGs in potential UPECs were different following disinfection, i.e., UV appears to have had no effect, while PAA significantly reduced the ARG levels. Thus, this study showed that both UV and PAA disinfections reduced the proportion of UPECs and that PAA disinfection also reduced the proportion of antimicrobial resistance gene-carrying UPEC pathotypes in municipal wastewaters.

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In VivoTransmission of an IncA/C Plasmid in Escherichia coli Depends on Tetracycline Concentration, and Acquisition of the Plasmid Results in a Variable Cost of Fitness

Applied and Environmental Microbiology ◽

10.1128/aem.04193-14 ◽

2015 ◽

Vol 81 (10) ◽

pp. 3561-3570 ◽

Cited By ~ 20

Author(s):

Timothy J. Johnson ◽

Randall S. Singer ◽

Richard E. Isaacson ◽

Jessica L. Danzeisen ◽

Kevin Lang ◽

...

Keyword(s):

Escherichia Coli ◽

High Dose ◽

Broad Host Range ◽

Antibiotic Administration ◽

Dose Administration ◽

Content Type ◽

E Coli ◽

The Impact ◽

Selection Of

ABSTRACTIncA/C plasmids are broad-host-range plasmids enabling multidrug resistance that have emerged worldwide among bacterial pathogens of humans and animals. Although antibiotic usage is suspected to be a driving force in the emergence of such strains, few studies have examined the impact of different types of antibiotic administration on the selection of plasmid-containing multidrug resistant isolates. In this study, chlortetracycline treatment at different concentrations in pig feed was examined for its impact on selection and dissemination of an IncA/C plasmid introduced orally via a commensalEscherichia colihost. Continuous low-dose administration of chlortetracycline at 50 g per ton had no observable impact on the proportions of IncA/C plasmid-containingE. colifrom pig feces over the course of 35 days. In contrast, high-dose administration of chlortetracycline at 350 g per ton significantly increased IncA/C plasmid-containingE. coliin pig feces (P< 0.001) and increased movement of the IncA/C plasmid to other indigenousE. colihosts. There was no evidence of conjugal transfer of the IncA/C plasmid to bacterial species other thanE. coli.In vitrocompetition assays demonstrated that bacterial host background substantially impacted the cost of IncA/C plasmid carriage inE. coliandSalmonella.In vitrotransfer and selection experiments demonstrated that tetracycline at 32 μg/ml was necessary to enhance IncA/C plasmid conjugative transfer, while subinhibitory concentrations of tetracyclinein vitrostrongly selected for IncA/C plasmid-containingE. coli. Together, these experiments improve our knowledge on the impact of differing concentrations of tetracycline on the selection of IncA/C-type plasmids.

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Extraintestinal Pathogenic and Antimicrobial-Resistant Escherichia coli, Including Sequence Type 131 (ST131), from Retail Chicken Breasts in the United States in 2013

Applied and Environmental Microbiology ◽

10.1128/aem.02956-16 ◽

2017 ◽

Vol 83 (6) ◽

Cited By ~ 15

Author(s):

James R. Johnson ◽

Stephen B. Porter ◽

Brian Johnston ◽

Paul Thuras ◽

Sarah Clock ◽

...

Keyword(s):

United States ◽

Escherichia Coli ◽

Virulence Genes ◽

Meat Products ◽

The United States ◽

Sequence Type ◽

The Other ◽

Antibiotic Resistant ◽

Content Type ◽

E Coli

ABSTRACT Chicken meat products are hypothesized to be vehicles for transmitting antimicrobial-resistant and extraintestinal pathogenic Escherichia coli (ExPEC) to consumers. To reassess this hypothesis in the current era of heightened concerns about antimicrobial use in food animals, we analyzed 175 chicken-source E. coli isolates from a 2013 Consumer Reports national survey. Isolates were screened by PCR for ExPEC-defining virulence genes. The 25 ExPEC isolates (12% of 175) and a 2:1 randomly selected set of 50 non-ExPEC isolates were assessed for their phylogenetic/clonal backgrounds and virulence genotypes for comparison with their resistance profiles and the claims on the retail packaging label (“organic,” “no antibiotics,” and “natural”). Compared with the findings for non-ExPEC isolates, the group of ExPEC isolates had a higher prevalence of phylogroup B2 isolates (44% versus 4%; P < 0.001) and a lower prevalence of phylogroup A isolates (4% versus 30%; P = 0.001), a higher prevalence of multiple individual virulence genes, higher virulence scores (median, 11 [range, 4 to 16] versus 8 [range, 1 to 14]; P = 0.001), and higher resistance scores (median, 4 [range, 0 to 8] versus 3 [range, 0 to 10]; P < 0.001). All five isolates of sequence type 131 (ST131) were ExPEC (P = 0.003), were as extensively resistant as the other isolates tested, and had higher virulence scores than the other isolates tested (median, 12 [range, 11 to 13] versus 8 [range, 1 to 16]; P = 0.005). Organic labeling predicted lower resistance scores (median, 2 [range, 0 to 3] versus 4 [range, 0 to 10]; P = 0.008) but no difference in ExPEC status or virulence scores. These findings document a persisting reservoir of extensively antimicrobial-resistant ExPEC isolates, including isolates from ST131, in retail chicken products in the United States, suggesting a potential public health threat. IMPORTANCE We found that among Escherichia coli isolates from retail chicken meat products purchased across the United States in 2013 (many of these isolates being extensively antibiotic resistant), a minority had genetic profiles suggesting an ability to cause extraintestinal infections in humans, such as urinary tract infection, implying a risk of foodborne disease. Although isolates from products labeled “organic” were less extensively antibiotic resistant than other isolates, they did not appear to be less virulent. These findings suggest that retail chicken products in the United States, even if they are labeled “organic,” pose a potential health threat to consumers because they are contaminated with extensively antibiotic-resistant and, presumably, virulent E. coli isolates.

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Estimating the Prevalence of Potential Enteropathogenic Escherichia coli and Intimin Gene Diversity in a Human Community by Monitoring Sanitary Sewage

Applied and Environmental Microbiology ◽

10.1128/aem.02747-13 ◽

2013 ◽

Vol 80 (1) ◽

pp. 119-127 ◽

Cited By ~ 12

Author(s):

Kun Yang ◽

Eulyn Pagaling ◽

Tao Yan

Keyword(s):

Escherichia Coli ◽

Virulence Genes ◽

Gene Diversity ◽

Content Type ◽

E Coli ◽

Enteric Diseases ◽

Detection Frequency ◽

Alternative Approach ◽

Prevalent Subtype ◽

Qpcr Quantification

ABSTRACTPresently, the understanding of bacterial enteric diseases in the community and their virulence factors relies almost exclusively on clinical disease reporting and examination of clinical pathogen isolates. This study aimed to investigate the feasibility of an alternative approach that monitors potential enteropathogenicEscherichia coli(EPEC) and enterohemorrhagicE. coli(EHEC) prevalence and intimin gene (eae) diversity in a community by directly quantifying and characterizing target virulence genes in the sanitary sewage. The quantitative PCR (qPCR) quantification of theeae,stx1, andstx2genes in sanitary sewage samples collected over a 13-month period detectedeaein all 13 monthly sewage samples at significantly higher abundance (93 to 7,240 calibrator cell equivalents [CCE]/100 ml) thanstx1andstx2, which were detected sporadically. The prevalence level of potential EPEC in the sanitary sewage was estimated by calculating the ratio ofeaetouidA, which averaged 1.0% (σ = 0.4%) over the 13-month period. Cloning and sequencing of theeaegene directly from the sewage samples covered the majority of theeaediversity in the sewage and detected 17 uniqueeaealleles belonging to 14 subtypes. Among them,eae-β2 was identified to be the most prevalent subtype in the sewage, with the highest detection frequency in the clone libraries (41.2%) and within the different sampling months (85.7%). Additionally, sewage and environmentalE. coliisolates were also obtained and used to determine the detection frequencies of the virulence genes as well aseaegenetic diversity for comparison.

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