Antimicrobial-Resistant Fecal Bacteria from Ceftiofur-Treated and Nonantimicrobial-Treated Comingled Beef Cows at a Cow-Calf Operation

Abstract

We compared the occurrences of 3rd-generation cephalosporin-resistant (3GC^r), tetracycline-resistant (TET^r), and trimethoprim-sulfamethoxazole-resistant (COT^r) Escherichia coli, 3GC^r and nalidixic acid-resistant (NAL^r) Salmonella enterica, and erythromycin-resistant (ERY^r) enterococci from the fecal samples of ceftiofur-treated (n = 162) and nonantimicrobial-treated (n = 207) comingled beef cows ≥8 years old, for which complete antimicrobial treatment records were available. The prevalence of 3GC^r (17%; n = 369), TET^r (88%), COT^r E. coli (22%), and ERY^r enterococci (69%) was 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. 3GC^r and NAL^r S. enterica were not detected. The prevalence of tetB was significantly (p < 0.05) higher compared with tetA among TET^r E. coli. However, the prevalence of tetA was significantly (p < 0.05) higher than tetB among 3GC^r and COT^r E. coli. There was a significant (p < 0.05) association between tetM and ermB among ERY^r enterococci. In conclusion, occurrences of 3GC^r, TET^r, and COT^r E. coli and ERY^r enterococci in comingled antimicrobial-treated and nonantimicrobial-treated beef cows were not associated with ceftiofur or other antimicrobial use, indicating that other factors influenced the observed levels of antimicrobial-resistant bacteria in feces of beef cows.

Keywords: E. coli; Salmonella; antimicrobial resistance; beef cows; ceftiofur; cephalosporin; enterococcus.