Population Dynamics of Salmonella enterica within Beef Cattle Cohorts Followed from Single-Dose Metaphylactic Antibiotic Treatment until Slaughter

Salmonella is a leading bacterial foodborne pathogen, causing a significant number of human infections and deaths every year in the United States. Macrolides and 3rd-generation cephalosporins play critical roles in the treatment of human salmonellosis. Use of these antibiotics in beef cattle can select for resistant bacteria that may enter the food chain or spread from the farm via manure. There is a lack of longitudinal research concerning the long-term effects of metaphylactic antibiotic administration. Here, we assessedSalmonella population dynamics during the feeding period until slaughter following single-dose antibiotic treatment. We found no long-term effects of antibiotic use early in the cattle-feeding period onSalmonella prevalence and antimicrobial resistance at slaughter. We identified the pens in which cattle were housed as the factor that contributed most toSalmonella serotypes being shared; importantly, the dominant strain in each pen changed repeatedly over the entire feeding period.