Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2015
Publication Date: 5/1/2015
Citation: Agga, G.E., Schmidt, J.W., Arthur, T.M. 2015. Antimicrobial resistance of enteric bacteria among ceftiofur treated and non-antimicrobial treated co-mingled pasture beef cows.[Abstract]. 4th American Society for Microbiology Conference on Antimicrobial Resistance in Zoonotic Bacteria and Foodborne Pathogens. S6:5, p.39.
Technical Abstract: Concerns have been raised that antimicrobial use in food animal production considerably increases antimicrobial resistance in bacteria. Due to their longevity, pasture beef cows are likely to be exposed to different antimicrobials that may create favorable conditions for antimicrobial resistant bacteria. Non-fed beef cattle constitute nearly 20% of the total domestic beef supply in the United States, but a higher proportion of ground beef comes from cows than fed cattle. We examined the occurrence of 3rd generation cephalosporin resistant (3GCr ) E. coli, tetracycline resistant (TETr) E. coli, trimethoprim-sulfamethoxazole resistant (COTr ) E. coli, 3GCr Salmonella enterica and erythromycin resistant (ERYr) enteroccoci from the fecal samples of 162 ceftiofur treated and 207 non-antimicrobial treated, co-mingled, pasture raised beef cows of = 8 years old in Nebraska. Among ceftiofur treated cows, 58% were treated with ceftiofur alone; the remaining 42% also received other antimicrobials (tetracyclines, penicillins, folate pathway inhibitors, phenicols, quinolones, or macrolides). The prevalence of 3GCr E. coli did not significantly differ (P = 0.41) between ceftiofur treated (15%) and non-antimicrobial treated (18%) cows. However, it significantly (P < 0.0001) declined over the birth cohorts from 47% in 2003 to 11% in 2006. Mean log10 CFU count of TETr E. coli was not associated with ceftiofur treatment, birth cohort, prior history of antimicrobial treatment or the length of time that lapsed between last antimicrobial treatment and sampling. The prevalence of TETr E. coli also did not significantly differ (P = 0.39) between ceftiofur treated (86%) and non-antimicrobial treated (90%) cows. However, it significantly (P = 0.01) increased in 2006 birth cohort compared to the older cohorts. The prevalence of COTr E. coli did not significantly (P = 0.50) differ by treatment group nor by birth cohort (P = 0.36). The prevalence of ERYr enterococci did not significantly differ (P = 0.60) between treatment groups (70% in non-antimicrobial treated cows versus 68% in the ceftiofur treated cows); however, it significantly declined (P = 0.05) from 2003 birth cohort to 2006 birth cohort. The prevalences of TETr E. coli, 3GCr E. coli, COTr E. coli and ERYr enterococci were not associated with prior history of antibiotic treatments or by the length of time that lapsed between last treatment and sampling. Salmonella was detected only from two cows and all the isolates were susceptible to 3rd-generation cephalosporins. In conclusion, occurrence of 3GCr E. coli, TETr E. coli, COTr E. coli and ERYr enterococci were not associated with ceftiofur treatments but were associated with birth cohorts in spite of being co-mingled. This indicates that factors other than antimicrobial use more strongly influenced the levels of antimicrobial-resistant bacteria in feces of non-fed beef cows.