Antimicrobial-resistant fecal bacteria from ceftiofur-treated and nonantimicrobial-treated comingled beef cows at a cow-calf operation

Authors: Agga, Getahun; Schmidt, John; Arthur, Terrance

Submitted to: Microbial Drug Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2016
Publication Date: 10/6/2016
Publication URL: https://handle.nal.usda.gov/10113/5700733
Citation: Agga, G.E., Schmidt, J.W., Arthur, T.M. 2016. Antimicrobial-resistant fecal bacteria from ceftiofur-treated and nonantimicrobial-treated comingled beef cows at a cow-calf operation. Microbial Drug Resistance. 22(7):598-608. doi:10.1089/mdr.2015.0259.

Interpretive Summary: There is a growing concern that antimicrobial use in food animals increases antimicrobial resistance in bacteria. Previous studies have shown that following antimicrobial treatment in fed cattle there is an increase in the antimicrobial-resistant bacterial population, which then returns to pre-treatment levels approximately 14 to 36 days after cessation of treatment. Cull beef and dairy cows contribute a significant proportion of meat destined for ground beef production, however, relative to dairy cows, there is a little information available on antimicrobial resistance in beef cows. Due to their longevity, beef cows are more likely to receive antimicrobial treatments than feedlot cattle, albeit spread over a longer period of time. We compared the occurrences of resistance to specific classes of antimicrobials in bacteria from the fecal samples of beef cows greater than or equal to 8 years old for which complete antimicrobial treatment records were available. Approximately half of the cows sampled for this study were treated with antimicrobials for the treatment of disease, while the other half did not receive any antimicrobial treatments over their lifetime. The prevalences of antimicrobial resistant bacteria were not associated with prior history of antimicrobial treatments or duration of time between last antimicrobial treatment and sampling. Since occurrences of antimicrobial resistance in comingled beef cows were not associated with antimicrobial use, other factors more strongly influenced the observed levels of antimicrobial-resistant bacteria in feces of beef cows.

Technical Abstract: We compared the occurrences of 3rd-generation cephalosporin-resistant (3GCr ), tetracycline-resistant (TETr) and trimethoprim-sulfamethoxazole-resistant (COTr ) Escherichia coli, 3GCr Salmonella enterica, nalidixic acid-resistant (NALr) S. enterica and erythromycin-resistant (ERYr) enterococci from the fecal samples of ceftiofur-treated (n = 162) and non-antimicrobial-treated (n = 207) comingled beef cows greater than or equal to 8 years old for which complete antimicrobial treatment records were available. The prevalences of 3GCr E. coli (17%; n = 369), TETr E. coli (88%), COTr E. coli (22%) and ERYr enterococci (69%) were not significantly (P > 0.05) associated with ceftiofur treatment, prior history of other antimicrobial treatments or duration of time between last antimicrobial treatment and sampling. 3GCr S. enterica and NALr S. enterica were not detected. The prevalence of tetB was significantly (P < 0.05) higher than that of tetA among TETr E. coli. However, the prevalence of tetA was significantly (P < 0.05) higher than tetB among 3GCr and COTr E. coli. tetM and ermB were significantly (P <0.05) associated among ERYr enterococci. In conclusion, occurrences of 3GCr, TETr and COTr E. coli, and ERYr enterococci in comingled beef cows were not associated with ceftiofur or other antimicrobial use indicating that other factors more strongly influenced the observed levels of antimicrobial-resistant bacteria in feces of beef cows.