Studies Performed in the Proper Context Suggest That Antimicrobial Use during Swine and Cattle Production Minimally Impact Antimicrobial Resistance

In the United States (U.S.) it is estimated that food-animal production agriculture accounts for >70% of antimicrobial (AM) use leading to concerns that agricultural uses are the primary source of antimicrobial resistance (AMR). Many studies report AMR in food-animal production settings without comparison to other environments. These types of studies lead to a false assumption that the AMR observed was due solely to the type and amount of AM used in the food-animal production setting. To determine, in the proper context, the impact of AM uses in U.S. cattle and swine production we performed a series of studies that incorporated culture-dependent and culture-independent methods. First, a study demonstrated that levels of antimicrobial-resistant bacteria were similar among beef cattle production waste, swine production waste, and human municipal wastewater treatment plant (WWTP) effluent. Interestingly, significantly higher levels of beta-lactam and fluoroquinolone resistance genes were detected in human municipal WWTP effluent. Additionally, multidrug resistant isolates were found in environments with little to no impact by human or food-animal wastes. Second, a study demonstrated that a 5-day in-feed chlortetracycline administration to cattle for the management of respiratory disease had minimal to no effect on AMR levels, especially long-term (> 27 days post treatment). Third, two studies were performed that examined the AMR impact of tylosin phosphate inclusion in cattle feed to prevent liver abscesses. In the first study, tylosin phosphate moderately increased the levels of erythromycin-resistant Enterococcus in feces and on the pen surface. In the second study, tylosin phosphate had no impact on levels of antimicrobial resistant bacteria in feces, on the pen surface, or on final carcasses. Fourth, a study of cecal contents obtained from 719 cattle during harvest, found generally similar AMR levels between cattle produced with and without antibiotics. Fifth, a study found generally similar AMR levels in ground beef (N = 370) and pork chops (N = 372) from animals produced with and without antibiotics. Although our data on swine production is less extensive than for beef, we conclude that antimicrobial use during U.S. beef and pork production does not broadly increase AMR in beef or pork products or their production environment. USDA is an equal opportunity provider and employer.