Temporal Shedding Patterns and Virulence Factors of Escherichia coli Serogroups O26, O103, O111, O145, and O157 in a Cohort of Beef Calves and Their Dams

This study investigated the shedding of Escherichia coli O26, O103, O111, O145, and O157 in a cohort of beef calves from birth over a 5-month period and assessed the relationship between shedding in calves and shedding in their dams, the relationship between shedding and scouring in calves, and the effect of housing on shedding in calves. Fecal samples were tested by immunomagnetic separation and by PCR and DNA hybridization assays. E. coli O26 was shed by 94% of calves. Over 90% of E. coli O26 isolates carried the vtx₁, eae, and ehl genes, 6.5% carried vtx₁ and vtx₂, and one isolate carried vtx₂ only. Serogroup O26 isolates comprised seven pulsed-field gel electrophoresis (PFGE) patterns but were dominated by one pattern which represented 85.7% of isolates. E. coli O103 was shed by 51% of calves. Forty-eight percent of E. coli O103 isolates carried eae and ehl, 2% carried vtx₂, and none carried vtx₁. Serogroup O103 isolates comprised 10 PFGE patterns and were dominated by two patterns representing 62.5% of isolates. Shedding of E. coli O145 and O157 was rare. All serogroup O145 isolates carried eae, but none carried vtx₁ or vtx₂. All but one serogroup O157 isolate carried vtx₂, eae, and ehl. E. coli O111 was not detected. In most calves, the temporal pattern of E. coli O26 and O103 shedding was random. E. coli O26 was detected in three times as many samples as E. coli O103, and the rate at which calves began shedding E. coli O26 for the first time was five times greater than that for E. coli O103. For E. coli O26, O103, and O157, there was no association between shedding by calves and shedding by dams within 1 week of birth. For E. coli O26 and O103, there was no association between shedding and scouring, and there was no significant change in shedding following housing.     

Longitudinal Emergence and Distribution of Escherichia coli O157 Genotypes in a Beef Feedlot

The purpose of this study was to describe the prevalence and longitudinal distribution of Escherichia coli O157 in feedlot cattle and the feedlot environment. Pen floors, water tanks, other cattle in the feedlot, feed, and bird feces were sampled for 2 weeks prior to entry of the study cattle. Twelve pens of study cattle were sampled twice weekly. At each sample time cattle feces, water from tanks in each pen, bunk feed, feed components, bird feces, and houseflies were collected. Bunk feed samples were collected before and after cattle had access to the feed. Overall, 28% of cattle fecal samples, 3.9% of bird fecal samples, 25% of water samples, 3.4% of housefly samples, 1.25% of bunk feed before calf access, and 3.25% of bunk feed samples after cattle had access to the feed were positive for E. coli O157. Genetic analysis of E. coli O157 isolates was done using pulsed-field gel electrophoresis (PFGE). PFGE types identified in sampling of the feedlot prior to calf entry were different than the majority of types identified following calf entry. A single strain type predominated in the samples collected after entry of the cattle. It was first identified 5 days after entry of the first pen of cattle and was subsequently identified in all pens. Data support that the incoming cattle introduced a new strain that became the predominant strain in the feedlot.     

Prevalence of Escherichia coli O157:H7 in Gallbladders of Beef Cattle

Gallbladders and rectal contents were collected from cattle (n = 933) at slaughter to determine whether the gallbladder harbors Escherichia coli O157:H7. Both gallbladder mucosal swabs and homogenized mucosal tissues were used for isolation. Only five gallbladders (0.54%) were positive for E. coli O157:H7. Fecal prevalence averaged 7.1%; however, none of the cattle that had E. coli O157:H7 in the gallbladder was positive for E. coli O157:H7 in feces. Therefore, the gallbladder does not appear to be a common site of colonization for E. coli O157:H7 in beef cattle.     

Comparison of diversities of Escherichia coli O157 shed from a cohort of spring-born beef calves at pasture and in housing

A cohort of spring-born beef calves demonstrated limited genetic and phenotypic diversity of Escherichia coli O157 when kept in a state of isolation. Despite this, there was a difference in the pulsed-field gel electrophoresis and phage types of isolates shed by cattle at pasture compared with those shed by the same cattle when weaned and housed.     

Detection of Escherichia coli O157:H7 in the Beef Marketed in Malaysia

Twelve strains of Escherichia coli O157:H7 were isolated from 9 of 25 beef samples purchased from retail stores in Malaysia. These strains produced Shiga toxin 2 with or without Shiga toxin 1 and had the eae gene and a 60-MDa plasmid. The antibiograms and the profiles of the arbitrarily primed PCR of the strains were diverse, suggesting that the strains may have originated from diverse sources.     

Prevalence of Escherichia coli O157:H7 in Organically and Naturally Raised Beef Cattle

We determined the prevalence of Escherichia coli O157:H7 in organically and naturally raised beef cattle at slaughter and compared antibiotic susceptibility profiles of the isolates to those of isolates from conventionally raised beef cattle. The prevalences of E. coli O157:H7 were 14.8 and 14.2% for organically and naturally raised cattle, respectively. No major difference in antibiotic susceptibility patterns among the isolates was observed.Many cattle producers have adopted production methods termed niche marketing to meet consumer demand for safe and healthy beef. The two main niches for beef cattle producers are organic and natural production (3). Organic beef cattle production, regulated by the U.S. Department of Agriculture, requires feeding with certified organic feed (16) and raising cattle without the use of antibiotics, hormones, and other veterinary products (3). Guidelines for producers to label the product as “natural” differ among natural beef programs, and such programs are administered and regulated by the company or organization that owns the brand name rather than the U.S. Department of Agriculture (11). Natural production guidelines often include a complete restriction on the use of antibiotics and growth-promoting hormones, but unlike guidelines for organic production, they allow feed from nonorganic sources (11). Escherichia coli O157:H7 is a major food-borne pathogen that causes outbreaks of hemorrhagic enteritis, which often leads to hemolytic uremic syndrome in children and the elderly (10). Cattle are major reservoirs of E. coli O157:H7, which colonizes the hindgut, specifically the rectoanal mucosal region. Cattle feces are the major source of food and water contamination (10). The impact of organic production methods on the prevalence of food-borne pathogens, including E. coli O157:H7 and Campylobacter spp. in dairy cattle (7, 14) and Campylobacter and Salmonella spp. in chickens (6, 19), has been studied previously. However, there is no published study on the prevalence of E. coli O157:H7 in organically and naturally raised beef cattle. Additionally, nothing is known regarding the effects of organic and natural production methods on the antibiotic susceptibilities of E. coli O157:H7 in beef cattle. Our objectives were to determine the prevalence of E. coli O157:H7 in the feces of organically and naturally raised beef cattle at slaughter and compare the antibiotic susceptibilities of isolates from organically, naturally, and conventionally raised beef cattle.Cattle included in this study were from three types of production systems, organic, natural, and conventional. Organically raised beef cattle were from farms that were certified by the National Organic Program (17). The naturally raised beef cattle were from farms that were certified by the All Natural Source Verified Beef Program (17). The collection of samples from these cattle occurred in an abattoir. Samples from conventionally raised cattle from two feedlots were collected in a different abattoir so that the antibiotic susceptibilities of their isolates could be compared with those of isolates from organically and naturally raised cattle. Fecal samples were obtained by cutting open the rectum and spooning out the contents. The mucosa of the rectum was then rinsed with water until free of visible fecal material and swabbed with a sterile foam-tipped applicator (4). The isolation and identification of E. coli O157 and PCR detection of major virulence genes (eae, stx₁, stx₂, hlyA, and fliC) were carried out as described by Reinstein et al. (13). A subset of 60 isolates, 20 (10 from fecal samples and 10 from rectoanal mucosal swabs [RAMS]) from each production system, was randomly chosen to determine the antibiotic susceptibility patterns by the broth microdilution method (9). The antibiotics (all from Sigma-Aldrich) tested were amikacin, amoxicillin (amoxicilline), ampicillin, apramycin, bacitracin, cefoxitin, ceftazidime, ceftriaxone, cephalothin (cefalotin), chloramphenicol, chlortetracycline, ciprofloxacin, enrofloxacin, erythromycin, florfenicol, gentamicin, kanamycin, lincomycin, monensin, nalidixic acid, neomycin, norfloxacin, novobiocin, oxytetracycline, penicillin, rifampin (rifampicin), spectinomycin, streptomycin, tetracycline, tilmicosin, trimethoprim, tylosin, and vancomycin. The MIC was defined as the lowest concentration of an antibiotic that prevented visible growth of the organism. Each concentration of the antibiotic compound was duplicated in the microtiter plate, and the MIC determination was repeated with a different inoculum preparation. Logistic regression was performed using the PROC GENMOD procedure in the SAS system (SAS Institute, Cary, NC) to compare the prevalences of E. coli O157:H7 (with binomial distribution of outcomes) in fecal samples, RAMS samples, and fecal or RAMS samples (overall animal level prevalence). The MICs of antibiotics for E. coli O157:H7 isolates were analyzed using a nonparametric survival test in the PROC LIFETEST program of SAS to determine the effects of the production system (natural, organic, or conventional). Data were right censored when necessary (when the organism was resistant to the highest concentration evaluated). The Wilcoxon test was utilized to determine the effect of the production system on MICs.Samples from a total of 553, 506, and 322 organically, naturally, and conventionally raised cattle, respectively, were collected. In organically raised cattle, the prevalence of E. coli O157:H7 in fecal samples ranged from 0 to 24.4% across sampling days, with an average of 9.3%, and the prevalence in RAMS ranged from 0 to 30.9%, with an average of 8.7% (Fig. ​(Fig.1).1). In naturally raised cattle, the prevalence of E. coli O157:H7 in fecal samples ranged from 0 to 20.3%, with an average of 7.2%, and the prevalence in RAMS ranged from 0 to 23.8%, with an average of 8.9% (Fig. ​(Fig.1).1). In both organically and naturally raised cattle, the prevalence (total) detected by both sampling methods together was greater (P < 0.05) than the prevalence detected by either method alone (Fig. ​(Fig.1).1). Samples (either feces or RAMS) from 36 (11.2%) of 322 conventionally raised feedlot cattle were culture positive for E. coli O157:H7. The fecal prevalence of E. coli O157:H7 was 6.5%, and the prevalence determined by the RAMS sampling method was 7.1%. Most isolates (66.7% from organically raised beef cattle and 77.8% from naturally raised beef cattle) were positive for eae, stx₂, hlyA, and fliC but negative for stx₁. The stx₂ gene was present in 100 and 95% of isolates from organically and naturally raised cattle, respectively. The prevalences of E. coli O157:H7 that we observed in organically and naturally raised beef cattle were similar to the previously reported prevalence in conventionally raised cattle (1). Our study did not include a statistical comparison of the prevalence data because of a number of differences, particularly in diet, among the organic, natural, and conventional production systems. Organically and naturally raised cattle are either required to graze a pasture or fed a forage-based diet. Although conflicting data exist (1), studies have shown that cattle fed a forage diet have both higher levels and longer durations of fecal shedding of E. coli O157:H7 than cattle fed a grain diet (18).Open in a separate windowFIG. 1.Prevalences of E. coli O157:H7 in organically and naturally raised beef cattle at slaughter. For each production system, bars not labeled with the same letter represent significantly different levels at P of <0.05.None of the tested isolates from the three production systems were susceptible to bacitracin, lincomycin, monensin, novobiocin, tilmicosin, tylosin, and vancomycin (MICs > 50 μg/ml). The MICs of 12 antibiotics (amikacin, apramycin, cefoxitin, ceftriaxone, gentamicin, kanamycin, nalidixic acid, neomycin, penicillin, rifampin, streptomycin, and tetracycline) for isolates collected from different production systems were significantly different (P < 0.05). MICs of gentamicin and neomycin for E. coli O157:H7 isolates from conventionally raised cattle were higher (P < 0.05) than those for isolates from naturally and/or organically raised cattle (Table ​(Table1).1). However, MICs of amikacin, apramycin, cefoxitin, ceftriaxone, kanamycin, nalidixic acid, penicillin, rifampin, and tetracycline for isolates from conventionally fed cattle were lower (P < 0.05) than those for isolates from naturally and/or organically raised cattle (Table ​(Table1).1). Among the 60 isolates tested for antibiotic susceptibilities, 6 isolates (10%) were susceptible to all antibiotics included in the study, excluding the seven antibiotics to which all isolates were resistant. Forty-two isolates (70%) were resistant to one antibiotic (MIC, >50 μg or >50 IU/ml), nine isolates (15%) were resistant to two antibiotics, and two isolates (3%) were resistant to five antibiotics. One isolate from the organically raised cattle group was resistant to 10 (amoxicillin, ampicillin, cefoxitin, cephalothin, chloramphenicol, florfenicol, oxytetracycline, penicillin, streptomycin, and tetracycline) of the 26 antibiotics that were inhibitory to other isolates. We have presented the data as the median MICs for each production system. In some instances, the median values were the same but the actual MIC data differed between production systems. This effect occurred because the data were right censored if isolates were not susceptible at 50 μg or 50 IU/ml. If more isolates from a particular production system than from another are censored, it may lead to statistical differences. This pattern justifies the use of survival analysis for this type of data. There were differences between MICs of many antibiotics (cefoxitin, ceftriaxone, gentamicin, nalidixic acid, neomycin, penicillin, rifampin, and tetracycline) for isolates from organically raised cattle and conventionally raised cattle. Similarly, there were differences between MICs of many antibiotics (amikacin, apramycin, ceftriaxone, kanamycin, nalidixic acid, and rifampin) for isolates from naturally raised cattle and conventionally raised cattle. For many of these antibiotics, MICs for isolates from organically or naturally raised cattle were greater than those for isolates from conventionally raised cattle. Resistance genes can be transferred among the enteric pathogen populations in food animals and humans (8), and it is possible that resistance genes from other bacteria in the gastrointestinal system of cattle may be acquired by E. coli O157:H7. For cattle, heavy metals like copper and zinc, which are also antimicrobial, are included in diets at concentrations in excess of the nutritional requirements, often replacing conventional antibiotics, to achieve growth promotion (5). Feeding with metals also results in the emergence of bacterial populations resistant to metals (5), which in some instances may lead to resistance to antibiotics. Mechanisms of resistance to copper at concentrations above those usually tolerated by normal cellular processes have been found on plasmids linked to resistance to antibiotics in some bacteria (5). Therefore, it is possible that isolates from organically or naturally raised cattle that are not exposed to antibiotics still may become resistant to antibiotics.

TABLE 1.

MICs of antimicrobials for E. coli O157:H7 isolates from conventionally, naturally, and organically raised beef cattle

Comparison of traditional and molecular typing methods of Escherichia coli O157

An account is given using typing methods and detection of virulence genes of different serotypes of Escherichia coli isolated in Hungary. By hybridization using SLT-I and SLT-II probes and PCR method using stx1-2, eae and ehx primers we could differentiate O157 strains of different serotypes into eight (stx, eae, ehxA positive; stx, eae positive; stx, ehxA positive; stx positive; eae, ehxA positive; eae positive; ehxA positive; stx, eae, ehxA negative) types. The discriminatory power of phage typing proves to be much higher than that of the plasmid profile. RAPD typing with different primers could confirm or exclude the subtypes identity of the isolated E. coli O157 serotypes. Escherichia coli O157:HNM isolates could be sorted in six different phage types and six different RAPD types with ERIC-1, in five RAPD types with ERIC-2 and in seven types with M13 primers. Escherichia coli O157:H7 showed six different phage types and three RAPD types with ERIC-1 and ERIC-2 and five types with M13 primers. According to our results the standard PFGE protocol [32] gives the opportunity to differentiate epidemiologically independent but evolutionary related or unrelated isolates, but the practical value of PFGE method for epidemiological purposes must be confirmed by other or more restriction enzymes or using an other protocol. Summarizing our results we suggest the use of phage and RAPD typing and in doubtful cases the PFGE method.     

Effect of Dietary Stress on Fecal Shedding of Escherichia coli O157:H7 in Calves

Two groups of calves were subjected to dietary stress by withholding of food beginning 1 or 14 days after inoculation with 10¹⁰ CFU of Escherichia coli O157:H7. Following treatment, neither group had a significant increase in fecal shedding of E. coli O157:H7. A third group of calves had food withheld for 48 h prior to inoculation with 10⁷ CFU of E. coli O157:H7. These calves were more susceptible to infection and shed significantly more E. coli O157:H7 organisms than calves maintained on a normal diet.     

Biocontrol of Escherichia coli O157 with O157-Specific Bacteriophages

Escherichia coli O157 antigen-specific bacteriophages were isolated and tested to determine their ability to lyse laboratory cultures of Escherichia coli O157:H7. A total of 53 bovine or ovine fecal samples were enriched for phage, and 5 of these samples were found to contain lytic phages that grow on E. coli O157:H7. Three bacteriophages, designated KH1, KH4, and KH5, were evaluated. At 37 or 4°C, a mixture of these three O157-specific phages lysed all of the E. coli O157 cultures tested and none of the non-O157 E. coli or non-E. coli cultures tested. These results required culture aeration and a high multiplicity of infection. Without aeration, complete lysis of the bacterial cells occurred only after 5 days of incubation and only at 4°C. Phage infection and plaque formation were influenced by the nature of the host cell O157 lipopolysaccharide (LPS). Strains that did not express the O157 antigen or expressed a truncated LPS were not susceptible to plaque formation or lysis by phage. In addition, strains that expressed abundant mid-range-molecular-weight LPS did not support plaque formation but were lysed in liquid culture. Virulent O157 antigen-specific phages could play a role in biocontrol of E. coli O157:H7 in animals and fresh foods without compromising the viability of other normal flora or food quality.     

Genotypic Analyses of Escherichia coli O157:H7 and O157 Nonmotile Isolates Recovered from Beef Cattle and Carcasses at Processing Plants in the Midwestern States of the United States

Escherichia coli O157:H7 and O157 nonmotile isolates (E. coli O157) previously were recovered from feces, hides, and carcasses at four large Midwestern beef processing plants (R. O. Elder, J. E. Keen, G. R. Siragusa, G. A. Barkocy-Gallagher, M. Koohmaraie, and W. W. Laegreid, Proc. Natl. Acad. Sci. USA 97:2999–3003, 2000). The study implied relationships between cattle infection and carcass contamination within single-source lots as well as between preevisceration and postprocessing carcass contamination, based on prevalence. These relationships now have been verified based on identification of isolates by genomic fingerprinting. E. coli O157 isolates from all positive samples were analyzed by pulsed-field gel electrophoresis of genomic DNA after digestion with XbaI. Seventy-seven individual subtypes (fingerprint patterns) grouping into 47 types were discerned among 343 isolates. Comparison of the fingerprint patterns revealed three clusters of isolates, two of which were closely related to each other. Remarkably, isolates carrying both Shiga toxin genes and nonmotile isolates largely fell into specific clusters. Within lots analyzed, 68.2% of the postharvest (carcass) isolates matched preharvest (animal) isolates. For individual carcasses, 65.3 and 66.7% of the isolates recovered postevisceration and in the cooler, respectively, matched those recovered preevisceration. Multiple isolates were analyzed from some carcass samples and were found to include strains with different genotypes. This study suggests that most E. coli O157 carcass contamination originates from animals within the same lot and not from cross-contamination between lots. In addition, the data demonstrate that most carcass contamination occurs very early during processing.     

Molecular Epidemiology of Antimicrobial-Resistant Commensal Escherichia coli Strains in a Cohort of Newborn Calves

Pulsed-field gel electrophoresis (PFGE) was used to investigate the dissemination and diversity of ampicillin-resistant (Amp^r) and nalidixic acid-resistant (Nal^r) commensal Escherichia coli strains in a cohort of 48 newborn calves. Calves were sampled weekly from birth for up to 21 weeks and a single resistant isolate selected from positive samples for genotyping and further phenotypic characterization. The Amp^r population showed the greatest diversity, with a total of 56 different genotype patterns identified, of which 5 predominated, while the Nal^r population appeared to be largely clonal, with over 97% of isolates belonging to just two different PFGE patterns. Distinct temporal trends were identified in the distribution of several Amp^r genotypes across the cohort, with certain patterns predominating at different points in the study. Cumulative recognition of new Amp^r genotypes within the cohort was biphasic, with a turning point coinciding with the housing of the cohort midway through the study, suggesting that colonizing strains were from an environmental source on the farm. Multiply resistant isolates dominated the collection, with >95% of isolates showing resistance to at least two additional antimicrobials. Carriage of resistance to streptomycin, sulfamethoxazole, and tetracycline was the most common combination, found across several different genotypes, suggesting the possible spread of a common resistance element across multiple strains. The proportion of Amp^r isolates carrying sulfamethoxazole resistance increased significantly over the study period (P < 0.05), coinciding with a decline in the most common genotype pattern. These data indicate that calves were colonized by a succession of multiply resistant strains, with a probable environmental source, that disseminated through the cohort over time.     

Early Attachment Sites for Shiga-Toxigenic Escherichia coli O157:H7 in Experimentally Inoculated Weaned Calves

Weaned 3- to 4-month-old calves were fasted for 48 h, inoculated with 10¹⁰ CFU of Shiga toxin-positive Escherichia coli (STEC) O157:H7 strain 86-24 (STEC O157) or STEC O91:H21 strain B2F1 (STEC O91), Shiga toxin-negative E. coli O157:H7 strain 87-23 (Stx⁻ O157), or a nonpathogenic control E. coli strain, necropsied 4 days postinoculation, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of, and 1 day after inoculation). STEC O157 bacteria were recovered from feces, intestines, or gall bladders of 74% (40/55) of calves 4 days after they were inoculated with STEC O157. Colon and cecum were sites from which inoculum-type bacteria were most often recovered. Histologic lesions of attaching-and-effacing (A/E) O157⁺ bacteria were observed in 69% (38/55) of the STEC O157-inoculated calves. Rectum, ileocecal valve, and distal colon were sites most likely to contain A/E O157⁺ bacteria. Fecal and intestinal levels of STEC O157 bacteria were significantly higher and A/E O157⁺ bacteria were more common in DEX-treated calves than in nontreated calves inoculated with STEC O157. Fecal STEC O157 levels were significantly higher than Stx⁻ O157, STEC O91, or control E. coli; only STEC O157 cells were recovered from tissues. Identifying the rectum, ileocecal valve, and distal colon as early STEC O157 colonization sites and finding that DEX treatment enhances the susceptibility of weaned calves to STEC O157 colonization will facilitate the identification and evaluation of interventions aimed at reducing STEC O157 infection in cattle.     

Clearance of Escherichia coli O157:H7 Infection in Calves by Rectal Administration of Bovine Lactoferrin

Enterohemorrhagic Escherichia coli (EHEC) strains, of which E. coli O157:H7 is the best-studied serotype, are an important group of foodborne pathogens causing severe illness in humans worldwide. The main reservoirs for EHEC are ruminants, mostly cattle, which harbor the bacteria in their intestinal tracts without showing clinical symptoms. In this study, we used bovine lactoferrin, a natural occurring bactericidal and immunomodulating protein, as an antibacterial agent against EHEC infection in cattle. Nine 3-month-old Holstein-Friesian calves were experimentally infected with EHEC (strain NCTC12900). Three animals received a daily rectal spray treatment with bovine lactoferrin, three animals received an oral treatment, and three animals served as a control group. Blood samples were collected weekly and fecal samples twice weekly to monitor antibody responses and fecal excretion, respectively. Animals in the rectal group ceased shedding within 26 days of the experimental treatment and remained negative. This beneficial effect of bovine lactoferrin was not observed in the oral group, where animals were still shedding at the time of euthanasia (day 61). All groups developed serum responses, but no clear differences could be observed between the groups. However, the results indicate that the use of bovine lactoferrin as a rectal treatment can be a useful strategy to preclude further transmission of EHEC infections from cattle to humans.     

Biocontrol of Escherichia coli O157 with O157-specific bacteriophages.

Escherichia coli O157 antigen-specific bacteriophages were isolated and tested to determine their ability to lyse laboratory cultures of Escherichia coli O157:H7. A total of 53 bovine or ovine fecal samples were enriched for phage, and 5 of these samples were found to contain lytic phages that grow on E. coli O157:H7. Three bacteriophages, designated KH1, KH4, and KH5, were evaluated. At 37 or 4 degrees C, a mixture of these three O157-specific phages lysed all of the E. coli O157 cultures tested and none of the non-O157 E. coli or non-E. coli cultures tested. These results required culture aeration and a high multiplicity of infection. Without aeration, complete lysis of the bacterial cells occurred only after 5 days of incubation and only at 4 degrees C. Phage infection and plaque formation were influenced by the nature of the host cell O157 lipopolysaccharide (LPS). Strains that did not express the O157 antigen or expressed a truncated LPS were not susceptible to plaque formation or lysis by phage. In addition, strains that expressed abundant mid-range-molecular-weight LPS did not support plaque formation but were lysed in liquid culture. Virulent O157 antigen-specific phages could play a role in biocontrol of E. coli O157:H7 in animals and fresh foods without compromising the viability of other normal flora or food quality.     

Concentration and Prevalence of Escherichia coli O157 in Cattle Feces at Slaughter

The concentration and prevalence of Escherichia coli O157 in cattle feces at the time of slaughter was studied over a 9-week period from May to July 2002. Fecal samples (n = 589) were collected from the rectums of slaughtered cattle, and the animal-level prevalence rate was estimated to be 7.5% (95% confidence interval [CI], 5.4 to 9.6%) while the group prevalence was 40.4% (95% CI, 27.7 to 53.2%). Of the 44 infected animals detected, 9% were high shedders that contained E. coli O157 at concentrations of >10⁴ CFU g⁻¹. These 9% represented >96% of the total E. coli O157 produced by all animals tested. All isolates possessed the vt₂ gene, 39 had the eaeA gene, and a further five had the vt₁ gene also. The presence of high-shedding animals at the abattoir increases the potential risk of meat contamination during the slaughtering process and stresses the need for correctly implemented hazard analysis and critical control point procedures.     

Concentration and prevalence of Escherichia coli O157 in cattle feces at slaughter

The concentration and prevalence of Escherichia coli O157 in cattle feces at the time of slaughter was studied over a 9-week period from May to July 2002. Fecal samples (n = 589) were collected from the rectums of slaughtered cattle, and the animal-level prevalence rate was estimated to be 7.5% (95% confidence interval [CI], 5.4 to 9.6%) while the group prevalence was 40.4% (95% CI, 27.7 to 53.2%). Of the 44 infected animals detected, 9% were high shedders that contained E. coli O157 at concentrations of >10(4) CFU g(-1). These 9% represented >96% of the total E. coli O157 produced by all animals tested. All isolates possessed the vt(2) gene, 39 had the eaeA gene, and a further five had the vt(1) gene also. The presence of high-shedding animals at the abattoir increases the potential risk of meat contamination during the slaughtering process and stresses the need for correctly implemented hazard analysis and critical control point procedures.     

High-Level Genotypic Variation and Antibiotic Sensitivity among Escherichia coli O157 Strains Isolated from Two Scottish Beef Cattle Farms

Escherichia coli O157:H7 is a human pathogen that is carried and transmitted by cattle. Scotland is known to have one of the highest rates of E. coli O157 human infections in the world. Two hundred ninety-three isolates were obtained from naturally infected cattle and the environment on two farms in the Scottish Highlands. The isolates were typed by pulsed-field gel electrophoresis (PFGE) with XbaI restriction endonuclease enzyme, and 19 different variations in patterns were found. There was considerable genomic diversity within the E. coli O157 population on the two farms. The PFGE pattern of one of the observed subtypes matched exactly with that of a strain obtained from a Scottish patient with hemolytic-uremic syndrome. To examine the stability of an individual E. coli O157 strain, continuous subculturing of a strain was performed 110 times. No variation from the original PFGE pattern was observed. We found three indistinguishable subtypes of E. coli O157 on both study farms, suggesting common sources of infection. We also examined the antibiotic resistance of the isolated strains. Phenotypic studies demonstrated resistance of the strains to sulfamethoxazole (100%), chloramphenicol (3.07%), and at a lower rate, other antibiotics, indicating the preservation of antibiotic sensitivity in a rapidly changing population of E. coli O157.     

Absence of Escherichia coli O157 in a survey of wildlife from Trinidad and Tobago

Fecal, cloacal, or rectal swabs of free-ranging and captive mammalian and avian wildlife in Trinidad and Tobago were cultured for non-sorbitol fermenting Escherichia coli and tested for O157:H7 strains. Ability of E. coli strains to produce hemolysin and mucoid colonies also was investigated. Of 271 free-ranging mammals tested, 158 (58%) yielded E. coli; only one (< 1%) bacterial isolate was a non-sorbitol fermenter which was not agglutinated by O157 antiserum. All isolates were negative for hemolysin production and mucoid colonial growth. Two hundred and sixty-three (90%) of 293 free-flying birds were positive for E. coli and all isolates were sorbitol fermenters and negative for production of hemolysin and mucoid growth. Of 175 captive wild animals from individual backyard farms and a government demonstration farm, 145 (83%) yielded E. coli with four (2%) non-sorbitol fermenters; all were negative for O157 strains, hemolysin production, and mucoid colonial growth. Of 373 animals in a zoo, 250 (67%) were positive for E. coli with only two (0.5%) non-sorbitol fermenters. All strains were non-hemolytic and non-mucoid farms. It appears that free-ranging and captive avian and mammalian wildlife are not important reservoirs of O157:H7 strains of E. coli in Trinidad and Tobago.     

Immunomagnetic separation of Escherichia coli O26, O111 and O157 from vegetables

AIMS: Raw fruits and vegetables have been increasingly associated with human infections caused by Shiga toxin-producing Escherichia coli. This study evaluates the isolation and detection of E. coli O26, O111 and O157 from vegetable samples using immunomagnetic particles. METHODS AND RESULTS: Standard cultivation and immunomagnetic separation (IMS) procedures were compared. It was found that immunomagnetic particles could efficiently concentrate E. coli cells, detecting significantly more bacteria than with standard cultivation procedures. CONCLUSION: Bacteria were detected in 93-100% of the inoculated samples using the IMS procedure, but only 36-93% samples tested by standard cultivation procedures were found to be positive. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicate that E. coli O26, O111 and O157 immunomagnetic particles can be a very useful and efficient tool for the detection of E. coli strains in raw vegetables, and could probably be used with samples of animal origin.