Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2009
Publication Date: 8/18/2009
Citation: Edrington, T.S., Long, M., Ross, T.T., Thomas, J.D., Callaway, T.R., Anderson, R.C., Craddock, F., Salisbury, M.W., Nisbet, D.J. 2009. Prevalence and antimicrobial resistance profiles of Escherichia coli O157:H7 and Salmonella isolated from feedlot lambs. Journal of Food Protection. 72:1713-1717.
Interpretive Summary: Sheep, like cattle, may contain bacteria such as E. coli O157:H7 and Salmonella that can make people sick; however, very little research has looked at their prevalence in healthy sheep in the feedlot. In some instances, these bacteria are resistant to antibiotics used to kill them although we do not know what percentage are resistant to multiple antibiotics. We sampled sheep on multiple occasions in the feedlot and at slaughter. Results of this experiment showed that sheep are naturally-colonized with these pathogenic bacteria, and that their wool can be a potential source of carcass contamination. These bacteria were susceptible to antibiotics used in human medicine.
Technical Abstract: The present study examined the incidence of E. coli O157:H7 and Salmonella in feedlot lambs. Fifty-six feedlot lambs originating from eight different sheep farming operations were grouped in a single drylot pen, fed and managed as typical for a sheep feedlot in the southwestern United States. Fecal samples were collected on d 0, 46, 87, and 122 of the feeding period via rectal palpation. Wool samples (ventral midline) were collected one time only at the feedlot, immediately prior to shipping to the processing plant and following slaughter, carcass swabs were collected. All samples were shipped overnight to the laboratory in College Station, TX for bacterial culture of E. coli O157:H7, Salmonella and fecal coliforms and select isolates examined for antimicrobial susceptibility. Overall, the percentage of fecal and wool samples positive for E. coli O157:H7 averaged 9 and 18%, respectively. One carcass swab was E. coli O157:H7 positive. Of the 155 fecal samples collected 11 (7%) were Salmonella positive. Salmonella was detected in nearly 50% of the wool samples collected prior to slaughter while none of the carcasses were Salmonella positive 24 h post-slaughter. All isolates (E. coli O157:H7, Salmonella and fecal coliforms) were susceptible to ceftiofur, enrofloxacin and trimethoprim/sulphamethoxazole. In general, Salmonella and fecal coliform isolates were increasingly antibiotic resistant as the feeding period progressed. Resistant patterns in fecal E. coli O157:H7 isolated in later collections were largely similar to the first collection. One E. coli O157:H7 isolate cultured from a carcass swab was resistant to seven antibiotics and seven wool E. coli O157:H7 isolates were multi-drug resistant. Results of this research demonstrate that feedlot sheep, like cattle, are naturally-colonized with the foodborne pathogens E. coli O157:H7 and Salmonella and that wool can be a significant potential source of carcass contamination. However, in this research, in-plant processing procedures and intervention strategies were largely effective in preventing carcass contamination.