Aims: To determine the prevalence and concentration of Escherichia coli O157 shed in faeces at slaughter, by beef cattle from different production systems. Methods and Results: Faecal samples were collected from grass-fed (pasture) and lot-fed (feedlot) cattle at slaughter and tested for the presence of E. coli O157 using automated immunomagnetic separation (AIMS). Escherichia coli O157 was enumerated in positive samples using the most probable number (MPN) technique and AIMS and total E. coli were enumerated using Petrifilm. A total of 310 faecal samples were tested (155 from each group). The geometric mean count of total E. coli was 5 · 10 5 and 2AE5 · 10 5 CFU g )1 for lot-and grass-fed cattle, respectively. Escherichia coli O157 was isolated from 13% of faeces with no significant difference between grass-fed (10%) and lot-fed cattle (15%). The numbers of E. coli O157 in cattle faeces varied from undetectable (<3 MPN g )1 ) to 1AE1 · 10 5 MPN g )1 . Twenty-six (67%) of 39 O157 positive faeces had <10 MPN g )1 and three (8%) had counts between 10 3 -10 5 MPN g )1 . There was no significant difference between concentrations of E. coli O157 in the faeces of grass-fed or lot-fed cattle. Conclusion: The prevalence and numbers of E. coli O157 in the faeces of cattle at slaughter were not affected by the production systems evaluated in this study. Significance and Impact of the Study: Information on the prevalence and numbers of E. coli O157 can be used for formulating intervention strategies and in quantitative risk assessments.

Stx2d is a recently described Shiga toxin whose cytotoxicity is activated 10-to 1,000-fold by the elastase present in mouse or human intestinal mucus. We examined Shiga toxigenic Escherichia coli (STEC) strains isolated from food and livestock sources for the presence of activatable stx 2d . The stx 2 operons of STEC were first analyzed by PCR-restriction fragment length polymorphism (RFLP) analysis and categorized as stx 2 , stx 2c vha , stx 2c vhb , or stx 2d EH250 . Subsequently, the stx 2c vha and stx 2c vhb operons were screened for the absence of a PstI site in the stx 2A subunit gene, a restriction site polymorphism which is a predictive indicator for the stx 2d (activatable) genotype. Twelve STEC isolates carrying putative stx 2d operons were identified, and nucleotide sequencing was used to confirm the identification of these operons as stx 2d . The complete nucleotide sequences of seven representative stx 2d operons were determined. Shiga toxin expression in stx 2d isolates was confirmed by immunoblotting. stx 2d isolates were induced for the production of bacteriophages carrying stx. Two isolates were able to produce bacteriophages 1662a and 1720a carrying the stx 2d operons. RFLP analysis of bacteriophage genomic DNA revealed that 1662a and 1720a were highly related to each other; however, the DNA sequences of these two stx 2d operons were distinct. The STEC strains carrying these operons were isolated from retail ground beef. Surveillance for STEC strains expressing activatable Stx2d Shiga toxin among clinical cases may indicate the significance of this toxin subtype to human health.Shiga toxigenic Escherichia coli (STEC) isolates are important food-borne pathogens that exist as commensal bacteria of ruminant animals. Shiga toxins (Stxs) comprise an A subunit that carries the toxic function and a B-subunit pentamer that binds the toxin to the eukaryotic cell receptor (for a review, see reference 22). Studies have indicated that Stx type 2 (Stx2), encoded by the stx 2 operon, has an epidemiological relationship with the severe human disease conditions hemolytic-uremic syndrome and hemorrhagic colitis. In addition, toxins Stx2 and Stx2c, encoded by different genotypic subtypes of stx 2 , have also been associated with a greater severity of human disease. In contrast, the more recently described stx 2 genotype, stx 2d EH250 (26), is apparently of lesser clinical significance.The nomenclature designating the Stx2d EH250 subtype is complicated by the prior use of Stx2d to designate activatable Stx2 (16,18). Both Stx2d and Stx2d EH250 possess Ser291 and Glu297 residues in the Stx2A subunit toxin-coding region; however, only Stx2d is activatable. While STEC isolates carrying stx 2d EH250 are commonly found, particularly from sheep (8), very few reports describe activatable stx 2d genotype in STEC.Activatable stx 2d was originally detected in STEC strain B2F1. Two activatable operons, stx 2d1 and stx 2d2 , have been identified in the B2F1 (17). Prior to their designation as stx 2d1 and stx 2d2 , these opero...

Aims: To determine the numbers of Escherichia coli O157 present in the faeces of naturally infected cattle. Methods and Results: A combination of the most probable number (MPN) technique and automated immunomagnetic separation (AIMS) was used to enumerate E. coli O157 in cattle faeces from both pasture-fed and grain-fed animals. A total of 22 E. coli O157 positive faecal samples were enumerated for E. coli O157 (10 from pasture-fed and 12 from grain-fed animals). The numbers of E. coli O157 in cattle faeces varied from undetectable (<3 MPN g )1 of faeces) to 2AE4 · 10 4 MPN g )1 . There was no significant difference (P ¼ 0AE06) between the numbers of E. coli O157 in pasture-fed or grain-fed cattle faeces, although the geometric mean (antilog of the mean of log 10 transformed MPN values) was higher in grain-fed (130 MPN g )1 ) than in pasture-fed (13 MPN g )1 ). Conclusions:Although the number of samples tested is small, the results indicate that E. coli O157 make up a small proportion of the total E. coli population present in cattle faeces. Significance and Impact of the Study: Information on the numbers of E. coli O157 present in cattle will assist in developing more robust quantitative risk assessments and formulating intervention strategies.

Methods and Results: Automated immunomagnetic separation (AIMS) was used for detection and isolation of Salmonella enriched from cattle faeces. Salmonella were enumerated from positive samples using a combination of the Most Probable Number (MPN) technique and AIMS. A total of 310 faecal samples were tested, 155 were from lot-fed cattle and 155 from grass-fed cattle. Salmonella spp. were isolated from 21 (6AE8%) of the cattle and the prevalence amongst grass-fed cattle (4AE5%) was not significantly different to that found in lot-fed cattle (9%). Counts of Salmonella in positive faeces varied from <3 MPN g)1 of faeces to 2AE8 · 10 3 MPN g )1 and 71% of positive samples had counts <10 MPN g )1 faeces. There was no significant difference in the mean log 10 number of Salmonella in faeces of cattle from each production system. Conclusion: Low numbers of beef cattle were found to shed Salmonella at the time of slaughter and the prevalence and the associated faecal concentrations did not vary significantly with the pre-slaughter production system (grass or lot feeding). The faecal concentration of Salmonella in the majority of faeces was low (<10 MPN g )1 ) with few high concentrations up to 3 · 10 3 MPN g )1 , suggesting there may be a low risk of carcase contamination.Significance and Impact of the Study: Beef cattle do not appear to be a major source of entry of Salmonella into the human food chain and the quantitative information contained in this study can be used in quantitative assessments of the associated risk of human salmonellosis.

Salmonella prevalence and counts were estimated for samples from the oral cavity, hide, rumen, and feces of 100 cattle at slaughter and from the pre- and postchill carcasses of these cattle. Samples were collected from 25 consecutively slaughtered cattle from each of four unrelated groups slaughtered at a single abattoir on different days. Ten additional fecal samples from each group were collected from their respective abattoir holding pens prior to slaughter. The prevalence of Salmonella was estimated using automated immunomagnetic separation, and the counts were estimated using a combination of most probable number (MPN) and automated immunomagnetic separation. A total of 606 samples were collected with Salmonella isolated from 157 (26%), including 29% of oral cavities, 68% of hides, 16% of feces collected after evisceration, 25% of rumen samples, 2% of prechill carcasses, 3% of postchill carcasses, and 48% of feces collected from holding pens. The prevalence and count of Salmonella varied between the different groups of animals tested. The highest count obtained was from a rumen sample (1.1 x 10(4) MPN/g). Other counts were generally low, with a maximum count in feces collected after evisceration and in the abattoir holding pens of 93 and 23 MPN/g, respectively. The highest count on hides, in oral cavities, and on carcasses was 4.8 MPN/cm2, 23 MPN/g, and 0.31 MPN/cm2, respectively. Even though Salmonella was present on the hides and in the rumen and feces of at least one animal from each group of cattle, the processing of animals at this abattoir resulted in few contaminated carcasses, and when contamination occurred, Salmonella was detected at low numbers.