Escherichia coli O157:H7 and Non-O157 Shiga Toxin-producing E. coli in Healthy Cattle, Sheep and Swine Herds in Northern Spain

Survival of O157:H7 and non-O157 serogroups of Escherichia coli in bovine rumen fluid and bile salts

While Shiga toxin-producing Escherichia coli (STEC) reside asymptomatically within ruminants, particularly cattle, these strains pose a serious health risk to humans. Research related to STEC has historically focused upon O157:H7. However, with an increase in foodborne outbreaks of non-O157 origin and recent changes in testing for non-O157 by the U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS), there is now a critical need to understand the biological activity of non-O157 serogroups. The focus of this study was to determine whether variations exist in the ability of different serotypes of STEC to survive within bovine rumen fluid medium and bile salts. The results of this study demonstrated through viable plate count analysis that the five serotypes tested (O157:H7, O111:H8, O103:K.:H8, O145:H28, and O26:H11) were capable of growing in rumen fluid medium. However, the concentrations of the serotypes O103:K.:H8 and O26:H11 after 24 h were significantly less (p < 0.05) than that observed for the other serotypes tested. A significant decrease (p = 0.03) in the survival of O103:K.:H8 in 50 mg/mL of bovine bile salts in comparison to the other STEC strains tested was also observed. Collectively, these data suggest that non-O157 serogroups of E. coli respond differently to the environment of the bovine gastrointestinal tract. Further research is needed to elucidate how these differential physiological variations correlate with alterations in colonization success within ruminants and how they may impact human illnesses.

Molecular characterization of Shiga toxin-producing Escherichia coli isolated from ruminant and donkey raw milk samples and traditional dairy products in Iran

The aims of the current study were to detect the virulence factors and antibiotic resistance of Shiga toxin-producing E. coli, in animal milk and dairy products in Iran. After E. coli dentification with culture method, PCR assay were developed for detection of pathogenic genes, serotypes and antibiotic resistance genes of E. coli. Results showed that out of 719 samples, 102 (14.18%) were confirmed to be positive for E. coli and out of 102 positive samples, 17.64% were O26 and 13.72% were O157 and 1.96% were O91 and 1.96% were O145 serotypes. Totally, the prevalence of stx1 and papA genes were the highest while the prevalence of sfaS and fyuA were the lowest in the positive samples. PCR results showed that tetA, tetB were the highest (64.70%) and aac(3)-IV were the lowest (27.45%) antibiotic resistant genes in E. coli positive samples. Our study indicated that the isolated E. coli trains in these regions had a highest antibiotic resistance to tetracycline (58.82%) and the lowest to nitrofurantoin (3.92%). tetA gene and E. coli O157 serotype had highest and aac(3)-IV gene, and E. coli O145 serotype had a lowest frequency rates of antibiotics resistance genes, in the region.

Escherichia coli O157:H7 Outbreak Linked to Raw Milk Cheese in Quebec, Canada: Use of Exact Probability Calculation and Case-Case Study Approaches to Foodborne Outbreak Investigation

The analytical studies used to investigate foodborne outbreak are mostly case-control or retrospective cohort studies. However, these studies can be complex to perform and susceptible to biases. This article addresses basic principles of epidemiology, probability, and the use of case-case design to identify the source of an Escherichia coli O157:H7 outbreak linked to raw milk cheese consumption in Quebec, Canada; a small number of cases with the same pulsed-field gel electrophoresis (PFGE) profile were involved. Between 4 December 2008 and 15 January 2009, a cumulative total of 16 E. coli O157:H7 cases with the same PFGE profile were reported to Quebec public health authorities. Among the first six cases reported, three had consumed raw milk cheese from the same producer (cheese A). Raw milk cheese is consumed by about 2% of the Quebec population. By using the exact probability calculation, it was found that a significantly higher proportion of E. coli O157:H7 cases (with the specific PFGE profile) than expected had consumed cheese A (P &lt; 0.001). These computations were updated during the course of the investigation to include subsequent cases and gave the same results. A case-case study corroborated this result. This article considers alternative statistical and epidemiological approaches to investigate a foodborne outbreak—in particular with an exact probability calculation and case-case comparisons. This approach could offer a fast and inexpensive alternative to regular case-control studies to target public health actions, particularly during a foodborne outbreak.

Investigation of an Escherichia coli O145 outbreak in a child day-care centre--extensive sampling and characterization of eae- and stx1-positive E. coli yields epidemiological and socioeconomic insight

Background

On October 29^th 2009 the health authorities in the city of Trondheim, Norway were alerted about a case of Shiga toxin-positive E. coli (STEC) O145 in a child with bloody diarrhoea attending a day-care centre. Symptomatic children in this day-care centre were sampled, thereby identifying three more cases. This initiated an outbreak investigation.

Methods

A case was defined as a child attending the day-care centre, in whom eae- and stx₁- but not stx₂-positive E. coli O145:H28 was diagnosed from a faecal sample, with multilocus variable number of tandem repeat analysis (MLVA) profile identical to the index isolate. All 61 children, a staff of 14 in the day-care centre, and 74 close contacts submitted faecal samples. Staff and parents were interviewed about cases' exposure to foods and animals. Faecal samples from 31 ewes from a sheep herd to which the children were exposed were analyzed for E. coli O145.

Results

Sixteen cases were identified, from which nine presented diarrhoea but not haemolytic uremic syndrome (HUS). The attack rate was 0.26, and varied between age groups (0.13-0.40) and between the three day-care centre departments (0.20-0.50), and was significantly higher amongst the youngest children. Median duration of shedding was 20 days (0-71 days). Children were excluded from the day-care centre during shedding, requiring parents to take compassionate leave, estimated to be a minimum total of 406 days for all cases. Atypical enteropathogenic E. coli (aEPEC) were detected among 14 children other than cases. These isolates were genotypically different from the outbreak strain. Children in the day-care centre were exposed to faecal pollution from a sheep herd, but E. coli O145 was not detected in the sheep.

Conclusions

We report an outbreak of stx₁- and eae-positive STEC O145:H28 infection with mild symptoms among children in a day-care centre. Extensive sampling showed occurrence of the outbreak strain as well as other STEC and aEPEC strains in the outbreak population. MLVA-typing of the STEC-isolates strongly indicates a common source of infection. The study describes epidemiological aspects and socioeconomic consequences of a non-O157 STEC outbreak, which are less commonly reported than O157 outbreaks.

Molecular subtypes of Campylobacter spp., Salmonella enterica, and Escherichia coli O157:H7 isolated from faecal and surface water samples in the Oldman River watershed, Alberta, Canada

Campylobacter spp., Salmonella enterica, and Escherichia coli O157:H7 isolated from 898 faecal, 43 sewage, and 342 surface water samples from the Oldman River were characterized using bacterial subtyping methods in order to investigate potential sources of contamination of the watershed. Among these pathogens, Campylobacter spp. were the most frequently isolated from faecal, sewage, and surface water samples (266/895, 11/43, and 91/342, respectively), followed by Salmonella (67/898, 8/43, and 29/342, respectively), and E. coli O157:H7 (16/898, 2/43, and 8/342, respectively). Salmonella Rubislaw was the most common serovar isolated from water. This serovar was also isolated from two wild bird species. Most other serovars isolated from water were either not isolated from animals or were isolated from multiple species. E. coli O157:H7 was predominantly isolated from cattle. The most common phage-types of this pathogen from cattle were also the most common among water isolates, and there were exact pulsed field gel electrophoresis and comparative genomic fingerprint matches between cattle, sewage, and water isolates. Campylobacters were commonly isolated from surface waters and faeces from most animal species. Restriction fragment length polymorphism of the Campylobacter flaA gene identified several location and host species-specific (cattle, goose, pig) fingerprints. Molecular subtyping of these bacterial pathogens shows considerable promise as a tool for determining the sources of faecal pollution of water.

Prevalence of Stx phages in environments of a pig farm and lysogenic infection of the field E. coli O157 isolates with a recombinant converting Phage

The prevalence and nature of Shiga toxin (Stx)-producing Escherichia coli (STEC) and Stx phage were investigated in 720 swine fecal samples randomly collected from a commercial breeding pig farm in China over a 1-year surveillance period. Eight STEC O157 (1.1%), 33 STEC non-O157 (4.6%), and two stx-negative O157 (0.3%) isolates were identified. Fecal filtrates were screened directly for Stx phages using E. coli K-12 derivative strains MC1061 as indicator, yielding 15 Stx1 and 57 Stx2 phages. One Stx1 and eight Stx2 phages were obtained following norfloxacin induction of the eight field STEC O157 isolates. All Stx1 phages had hexagonal heads with long tails, while Stx2 phages had three different morphologies. Notably, most of field STEC O157 isolates released more free phages and Stx toxin after induction with ciprofloxacin. Furthermore, upon infection with the recombinant phage ΦMin27(Δstx::cat), E. coli laboratory strains produced both lysogenic and lytic phage, whereas two of the eight O157 STEC isolates produced only lysogens. The lysogens from laboratory strains produced infectious particles similar to ΦMin27. Similarly, the lysogens from the STEC O157 isolates released Stx phage too, although free ΦMin27(Δstx::cat) particles were not detected. Collectively, our results reveal that breeding pig farms could be important reservoirs for Stx phages and that residual antibacterial agents may enhance the release of Stx phages and the expression of Stx.

Temporal and spatial patterns of bovine Escherichia coli O157 prevalence and comparison of temporal changes in the patterns of phage types associated with bovine shedding and human E. coli O157 cases in Scotland between 1998-2000 and 2002-2004

Background

Escherichia coli O157 is an important cause of acute diarrhoea, haemorrhagic colitis and, especially in children, haemolytic uraemic syndrome (HUS). Incidence rates for human E. coli O157 infection in Scotland are higher than most other United Kingdom, European and North American countries. Cattle are considered the main reservoir for E. coli O157. Significant associations between livestock related exposures and human infection have been identified in a number of studies.

Results

Animal Studies: There were no statistically significant differences (P = 0.831) in the mean farm-level prevalence between the two studies (SEERAD: 0.218 (95%CI: 0.141-0.32); IPRAVE: 0.205 (95%CI: 0.135-0.296)). However, the mean pat-level prevalence decreased from 0.089 (95%CI: 0.075-0.105) to 0.040 (95%CI: 0.028-0.053) between the SEERAD and IPRAVE studies respectively (P < 0.001). Highly significant (P < 0.001) reductions in mean pat-level prevalence were also observed in the spring, in the North East and Central Scotland, and in the shedding of phage type (PT) 21/28. Human Cases: Contrasting the same time periods, there was a decline in the overall comparative annual reported incidence of human cases as well as in all the major PT groups except 'Other' PTs. For both cattle and humans, the predominant phage type between 1998 and 2004 was PT21/28 comprising over 50% of the positive cattle isolates and reported human cases respectively. The proportion of PT32, however, was represented by few (<5%) of reported human cases despite comprising over 10% of cattle isolates. Across the two studies there were differences in the proportion of PTs 21/28, 32 and 'Other' PTs in both cattle isolates and reported human cases; however, only differences in the cattle isolates were statistically significant (P = 0.002).

Conclusion

There was no significant decrease in the mean farm-level prevalence of E. coli O157 between 1998 and 2004 in Scotland, despite significant declines in mean pat-level prevalence. Although there were declines in the number of human cases between the two study periods, there is no statistically significant evidence that the overall rate (per 100,000 population) of human E. coli O157 infections in Scotland over the last 10 years has altered. Comparable patterns in the distribution of PTs 21/28 and 32 between cattle and humans support a hypothesized link between the bovine reservoir and human infections. This emphasizes the need to apply and improve methods to reduce bovine shedding of E. coli O157 in Scotland where rates appear higher in both cattle and human populations, than in other countries.

Prevalence and concentration of Verotoxigenic Escherichia coli O157:H7 in adult sheep at slaughter from Italy

A 1-year study on the animal-level prevalence and concentration of Escherichia coli O157 in adult sheep at slaughter was performed, to collect qualitative and quantitative information on the diffusion of the pathogen in adult sheep from Italy. A total 533 samples were collected, with a similar distribution in the four seasons. For prevalence estimates, a simple random sampling technique was used. An immuno-magnetic separation technique was used for sample screening, with enumeration of the pathogen in positive samples, along with molecular and serological identification of isolates. An overall prevalence of 7.1% (38/ 533, 95% CI 4.9-9.3%) was observed for fully virulent E. coli O157. A wide interval of VTEC O157 per gram was observed (< 100 to 6 x 10(5) CFU g(-1)), with 28.9% (11/38) of positive samples > or = 1 x 10(3) CFU g(-1), set as the threshold for those animals defined 'active shedders' for the purpose of the study. Eight per cent (3/38) of animals shed > 1 x 10(4) g(-1) VTEC O157, which represents > 96% of the total VTEC O157 bacteria cultured from all animals tested. The prevalence estimate of active shedders was therefore 2.1% (95% CI 0.9-3.3%). Most (34/38, 89.5%) of the positive animals were found in summer (July-September). Prevalence and concentrations of virulent VTEC O157 obtained in this study contribute to the demonstration that adult sheep represent a relevant source of environmental contamination from virulent VTEC O157, as well as a source of VTEC O157 contamination for food of ovine origin (meat and dairy products), especially during warm months.

Comparison of enrichment procedures for shiga toxin-producing Escherichia coli in wastes from commercial swine farms

Three methods for enrichment of Shiga toxin-producing Escherichia coli (STEC) were compared using waste pit samples from swine production facilities housing 50 to 3,000 animals. The STEC gene stx2 was detected in 5 of 17 pooled samples using a U.S. Department of Agriculture (USDA) enrichment procedure, 6 of 17 samples using a U.S. Food and Drug Administration (FDA) enrichment procedure, and 8 of 17 samples using an experimental acid enrichment. All isolates were non-O157 and 5 of 6 were positive for enterotoxigenic E. coli-associated heat stable toxins a and b. The three enrichment procedures were also tested for their ability to support growth of 31 strains of STEC. The acid enrichment media supported growth of 100% of the strains, the FDA medium supported 77% of the strains, and the USDA medium supported 16% of the strains.

Occurrence, virulence genes and antibiotic resistance of Escherichia coli O157 isolated from raw bovine, caprine and ovine milk in Greece

The examination of 2005 raw bovine (n = 950), caprine (n = 460) and ovine (n = 595) bulk milk samples collected throughout several regions in Greece for the presence of Escherichia coli serogroup O157 resulted in the isolation of 29 strains (1.4%) of which 21 were isolated from bovine (2.2%), 3 from caprine (0.7%) and 5 from ovine (0.8%) milk. Out of the 29 E. coli O157 isolates, only 12 (41.4%) could be classified as Shiga-toxigenic based on immunoassay and PCR results. All 12 Shiga-toxigenic E. coli serogroup O157 isolates belonged to the E. coli O157:H7 serotype. All except one of the 12 Shiga-toxin positive isolates were stx(2)-positive, five of which were also stx(1)-positive. The remaining isolate was positive only for the stx(1) gene. All stx-positive isolates (whether positive for stx(1), stx(2) or stx(1) and stx(2)) were also PCR-positive for the eae and ehxA genes. The remaining 17 E. coli O157 isolates (58.6%) were negative for the presence of the H7 flagellar gene by PCR, tested negative for Shiga-toxin production both by immunoassay and PCR, and among these, only four and three strains were PCR-positive for the eae and ehxA genes, respectively. All 29 E. coli O157 isolates displayed resistance to a wide range of antimicrobials, with the stx-positive isolates being, on average, resistant to a higher number of antibiotics than those which were stx-negative.

Host range and lytic capability of four bacteriophages against bovine and clinical human isolates of Shiga toxin-producing Escherichia coli O157:H7

AIMS

To evaluate host range and lytic capability of four bacteriophages (rV5, wV7, wV8 and wV11) against Escherichia coli O157:H7 (STEC O157:H7) from cattle and humans.

METHODS AND RESULTS

Four hundred and twenty-two STEC O157:H7 isolates (297 bovine; 125 human) were obtained in Alberta, Canada. The four phages were serially diluted and incubated for 5 h with overnight cultures of STEC O157:H7 to estimate their multiplicity of infection (MOI). All bovine STEC O157:H7 were subjected to pulsed-field gel electrophoresis (PFGE) and phage typing (PT). Phage wV7 lysed all human and bovine isolates irrespective of PFGE genotype or PT phenotype and exhibited the lowest MOI (0.004-0.006, P < 0.0001) of all phages. Phages rV5 and wV11 exhibited a lower MOI (0.002-0.04, P < 0.0001) than did phage wV8 (25-29) and they had a narrower host range than wV7 or wV8. Phages rV5, wV11 and wV8 lysed 342 (81.0%), 321 (76.1%) and 407 (96.4%), respectively, of the 422 isolates. Susceptibility of bovine STEC O157:H7 to rV5, w11 and wV8 was influenced by PFGE genotype and/or PT phenotype.

CONCLUSIONS

Phages exhibited activity against the majority of bovine and human STEC O157:H7 isolates. PFGE genotype and/or PT phenotype of the host-target influenced their vulnerability to phage attack. Susceptibility of bovine STEC O157:H7 to phage may also differ among farms. Both lytic capability and host range should be considered in the selection of therapeutic phage for on-farm control of STEC O157:H7.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present work indicates that a four-phage cocktail should be equally effective at mitigating STEC O157:H7 isolates both of bovine and of human origin. Given that some STEC O157:H7 exhibited resistance to some but not all phages, a phage cocktail is the logical approach to efficacious on-farm therapy.

Escherichia coli O157:H7 colonization in small domestic ruminants

Enterohaemorrhagic Escherichia coli O157:H7 was first implicated in human disease in the early 1980s, with ruminants cited as the primary reservoirs. Preliminary studies indicated cattle to be the sole source of E. coli O157:H7 outbreaks in humans; however, further epidemiological studies soon demonstrated that E. coli O157:H7 was widespread in other food sources and that a number of transmission routes existed. More recently, small domestic ruminants (sheep and goats) have emerged as important sources of E. coli O157:H7 human infection, particularly with the widespread popularity of petting farms and the increased use of sheep and goat food products, including unpasteurized cheeses. Although the colonization and persistence characteristics of E. coli O157:H7 in the bovine host have been studied intensively, this is not the case for small ruminants. Despite many similarities to the bovine host, the pathobiology of E. coli O157:H7 in small domestic ruminants does appear to differ significantly from that described in cattle. This review aims to critically review the current knowledge regarding colonization and persistence of E. coli O157:H7 in small domestic ruminants, including comparisons with the bovine host where appropriate.

Super-shedding and the link between human infection and livestock carriage of Escherichia coli O157

Cattle that excrete more Escherichia coli O157 than others are known as super-shedders. Super-shedding has important consequences for the epidemiology of E. coli O157 in cattle--its main reservoir--and for the risk of human infection, particularly owing to environmental exposure. Ultimately, control measures targeted at super-shedders may prove to be highly effective. We currently have only a limited understanding of both the nature and the determinants of super-shedding. However, super-shedding has been observed to be associated with colonization at the terminal rectum and might also occur more often with certain pathogen phage types. More generally, epidemiological evidence suggests that super-shedding might be important in other bacterial and viral infections.