Apparent prevalence and selected risk factors of methicillin-resistant Staphylococcus aureus and non-aureus staphylococci and mammaliicocci in bulk tank milk of dairy herds in Indiana, Ohio, and Michigan

Summary: Antimicrobial resistance in agriculture poses potential health risks to animals and humans, making it a serious concern among both consumers and scientists. Non-aureus staphylococci and mammaliicocci (NASM) are a highly diverse group of bacteria that are frequently recovered from bulk tank milk (BTM) as well as intramammary infections. This is significant because methicillin-resistant (MR) NASM may serve as a reservoir of resistant genes that pose a risk to humans and animals. The aim of this study was to determine the prevalence of MR Staphylococcus aureus and NASM in 300 BTM samples collected from farms across Michigan, Ohio, and Indiana. No MR S. aureus were identified; however, 4.3% of BTM contained MR NASM. Dairy farms with ≤200 lactating cows that had swine located on the farm had a higher prevalence of MR NASM than larger farms that did not contain swine.