Factors contributing to the presence of Escherichia coli O157:H7 and O157:NM in feedlots and feedlot cattle.



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Texas A&M University


Environmental sources within 5 feedlots were sampled for E. coli O157:H7 and O157:NM to determine the prevalence of this pathogen with a view to minimize or control its spread in the feedlot environment. Monthly samples were taken from the feedlots in the Panhandle and South Plains of Texas over a nine-month period. Samples were examined by an immunomagnetic bead separation, followed by plating onto CT-SMAC and CHROMagar O157 media. Sorbitol-negative colonies were tested using ImmunoCard Stat! E. coli O157:H7 Plus and confirmed as E. coli O157:H7, using biochemical (Vitek system) and serological tests (latex agglutination). Additionally, one hundred sponge samples were collected from the hides of stunned cattle at the slaughter plant. All isolates were subjected to rep-PCR DNA fingerprinting and antimicrobial profiling. E. coli O157 was isolated from hide (56%) and environmental samples (4%). E. coli O157 was isolated from all environmental sources, with peak prevalence during November (9%) and March (10%). At least one sample from each feedlot was positive 42% of the time. The most contaminated sites were the chute area (6%) and sludge from waste water ponds (6%). Positive samples were most frequently found from feedlot 5 (7%) and the greatest variation in positive samples between feedlots (0-34%) occurred during March. A decrease in the presence of E. coli O157 in feedlots was observed during January (0%), when ambient, water, and pond sludge temperatures were consistently low. No correlation with other environmental factors was observed. Hide was a primary source of E. coli O157 on carcasses with an overall prevalence of 56%. Of two sampling days, the number of positive hide samples varied from 14% for the first day to 98% for the second day. The total positive samples collected (environmental (47); hide (56)) were 64% H7, and 36% NM. The environmental isolates showed similar antibiotic resistance patterns, regardless of the source. Most E. coli O157 isolates from the feedlots and hides showed a high level of resistance to cephalothin (45%) and sulfisoxazole (56%). E. coli O157 isolates from feedlots were resistant to more than 10 antibiotics (9/317). All of the isolates appeared highly similar, with an average similarity of 53% by rep-PCR DNA fingerprinting.