Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2009
Publication Date: 12/16/2009
Citation: Edrington, T.S., Farrow, R.L., Loneragan, G., Ives, S., Engler, M., Wagner, J., Corbin, M., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2009. Influence of beta-agonists (ractopamine HCl and zilpaterol HCl) on fecal shedding of Escherichia coli O157:H7 in feedlot cattle. Journal of Food Protection. 72:2587-2591.
Interpretive Summary: Ractopamine and zilpaterol are compounds fed to cattle prior to slaughter to improve performance and increase carcass leanness. Ractopamine is similar to some hormones that have been shown to affect the growth of E. coli O157:H7. The objectives of the present studies were to determine if ractopamine or zilpaterol influence fecal shedding of E. coli and Salmonella when fed to feedlot cattle. Results showed that neither ractopamine or zilpaterol had a significant effect on E. coli O157 or Salmonella fecal prevalence in cattle immediately prior to slaughter. As this compound is fed immediately prior to slaughter, the lack of any adverse effect on pathogenic bacteria shedding is good news.
Technical Abstract: The effects of two beta-agonists [ractopamine hydrochloride (Optaflexx**R) and zilpaterol hydrochloride (Zilmax**R)], recently approved for use in feedlot cattle to improve performance traits and carcass leanness, were examined on fecal shedding of E. coli O157:H7 in feedlot cattle. Fecal samples (n = 2454) were obtained from four experiments (one Optaflexx**R, three Zilmax**R) over the course of a three-year period either by rectal palpation (Optaflexx**R experiment) or from pen-floor fecal pats. Samples were shipped overnight for quantitative and qualitative (immunomagnetic separation technique) culture of E. coli O157:H7. Salmonella was cultured, and select isolates (E. coli O157:H7 and Salmonella) were examined for antimicrobial susceptibility in the final Zilmax**R experiment. No significant treatment differences were detected for fecal prevalence of E. coli O157:H7, the percentage of E. coli 0157:H7 positive animals per pen or in pen status (percentage of pens with at least one animal shedding E. coli O157:H7) in the Optaflexx**R experiment, although a slight trend (P = 0.12) was observed for decreased fecal prevalence when comparing Control (17.4% positive) and Optaflexx**R (13.5% positive) treatments. Zilmax**R feeding had no effect (P greater than 0.20) on fecal shedding or pen status in the first or second experiments, with overall E. coli O157:H7 prevalence relatively low (less than 7%). The percentage of fecal samples E. coli O157:H7 positive following qualitative culture was higher (P less than 0.05) in the Zilmax**R treatment (10.3% versus 6.1% for Control and Zilmax**R treatments, respectively). The percentage of E. coli O157:H7 positive samples within a pen and the percentage of E. coli O157:H7 positive pens were not different (P greater than 0.10) among treatments. The percentage of fecal samples Salmonella positive following direct plating and enrichment was higher (P less than 0.05) in the Control compared to the Zilmax**R treatment (19.4% versus 13.1%, respectively) when combined across collections (see Table 4); however, Salmonella fecal concentrations were not different (P greater than 0.10). No significant treatment differences were observed for the percentage of Salmonella positive samples within a pen or for the percentage of Salmonella positive pens. Results of the antimicrobial susceptibility testing on E. coli O157:H7 (n = 16) and Salmonella (n = 32) isolates demonstrated that the majority (90%) of the isolates examined were susceptible to all antimicrobials on the NARM’s panel. Five isolates (4 Salmonella, 1 E. coli O157:H7; 3 from control and 2 from Zilmax**R treatments) were resistant to one antibiotic each, and none of the tested isolates were multi-drug resistant. The slight, or lack of an adverse effect, of beta-agonists on fecal shedding of the foodborne pathogens E. coli O157:H7 and Salmonella is good news from a food safety standpoint as these compounds are fed immediately prior to slaughter to improve feedlot performance and carcass leanness.