A survey was performed to estimate the frequency of enterohemorrhagic Escherichia coli O157:H7 or O157:nonmotile (EHEC O157) in feces and on hides within groups of fed cattle from single sources (lots) presented for slaughter at meat processing plants in the Midwestern United States, as well as frequency of carcass contamination during processing from cattle within the same lots. Of 29 lots sampled, 72% had at least one EHEC O157-positive fecal sample and 38% had positive hide samples. Overall, EHEC O157 prevalence in feces and on hides was 28% (91 of 327) and 11% (38 of 355), respectively. Carcass samples were taken at three points during processing: preevisceration, postevisceration before antimicrobial intervention, and postprocessing after carcasses entered the cooler. Of 30 lots sampled, 87% had at least one EHEC O157-positive preevisceration sample, 57% of lots were positive postevisceration, and 17% had positive postprocessing samples. 43% (148 of 341), 18% (59 of 332) and 2% (6 of 330), respectively. Reduction in carcass prevalence from preevisceration to postprocessing suggests that sanitary procedures were effective within the processing plants. Fecal and hide prevalence were significantly correlated with carcass contamination (P ‫؍‬ 0.001), indicating a role for control of EHEC O157 in live cattle. Prevalence of EHEC O157 in the three postprocessing samples wasAbbreviation: EHEC, enterohemorrhagic Escherichia coli.

Aims: To explore the effect of drug-free poultry production on the intestinal microflora of broiler chickens, the bacterial community of this environment was quantitatively profiled in both conventionally reared birds and birds reared without antibiotic growth promotants (AGPs) on a vegetable-based diet. Methods and Results: Quantitative, real-time PCR with group-specific 16S rDNA primer sets was used to enumerate the abundance of the following chicken gastrointestinal (GI) tract phylogenetic groups: the Clostridium leptumFaecalibacterium prausnitzii subgroup (Clostridium genus cluster IV), the Clostridium coccoides -Eubacterium rectale subgroup (Clostridium cluster XIVa and XIVb), the Bacteroides group (including Prevotella and Porphyromonas), Bifidobacterium spp., the Enterobacteriaceae, the Lactobacillus group (including the genera Leuconostoc, Pediococcus, Aerococcus and Weissella), the Clostridium perfringens subgroup (Clostridium cluster I), Enterococcus spp., Veillonella spp., Atopobium spp., Campylobacter spp. and the domain Bacteria. A species-specific 5¢-nuclease (Taqman) assay was also employed to specifically assess Cl. perfringens abundance. Ten birds were sampled from each of two commercial chicken houses, one in which feed was supplemented with AGPs and exogenous animal protein, and the other vegetable-based and drug-free, at 7, 14 and 21 days of age. The ileal community was dominated by two large populations, the lactobacilli and the Enterobacteriaceae, with those taxa much more numerous in drugfree vegetable-based diet fed birds than those conventionally reared at the 7-and 14-day time periods. The progressive changes in microflora in both the conventional and drug-free caeca were similar to each other, with the Enterobacteriaceae sequences dominating at day 7, but being replaced by obligate anaerobe signature sequences by day 14. Of note was the finding that all the day 14 and day 21 replicate caecal samples from the drug-free house were positive for Campylobacter spp. averaging >10 8 16S rDNA gene copies per gram wet weight. Conclusions: Quantitative, real-time PCR indicates that the effects of drug-free rearing on the chicken GI tract microbial community are most pronounced in the ileal region, but AGPs may be important in controlling Campylobacter colonization of the caecum. Significance and Impact of the Study: A quantitative taxonomic understanding of the shifting microbial ecology of the broiler chicken gut microbiota is important in the light of AGP withdrawal. AGP withdrawal has occurred in response to concerns over the transfer of antimicrobial-resistant bacteria to humans via the food production chain.