Assessing the Prevalence of Methicillin-Resistant Staphylococcus aureus (MRSA) in Pigs from the Fort Hays State University (FHSU) Animal Farm Swine Unit

Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen that primarily colonizes the nasal passages and skin of humans and animals as a commensal organism, but it can also cause a wide range of infections. This study aimed to determine the current prevalence of MRSA within the pig herd at the FHSU animal farm and its surrounding environments over a four-month period. A total of 80 samples were collected from pigs and the environment at the FHSU animal farm between February and May 2023. Of these, 73 (93%) produced presumptive MRSA colonies (mauve colonies) on CHROMagar MRSA II, a selective and differential medium for MRSA. Among all samples, 41 (51%) yielded mannitol-fermenting, catalase-positive isolates consistent with Staphylococcus aureus. Subsequent antimicrobial susceptibility testing by the Kirby-Bauer disk diffusion method showed that 13 (31%) of these 41 isolates were resistant to oxacillin, indicating potential MRSA. Of the 13 oxacillin-resistant isolates, eight representing distinct resistance patterns were selected for DNA sequencing due to resource constraints. DNA sequencing revealed that five of the eight oxacillin-resistant isolates were Staphylococcus lentus, while the remaining three were Bacillus cereus, Bacillus thuringiensis and Pantoea vagans. Although these organisms exhibited oxacillin resistance, none were confirmed as MRSA. These findings indicate that there were no cases of MRSA on the pig farm. However, the presence of non-S. aureus species with antimicrobial resistance suggests they may contribute to the overall resistance burden of the farm. The potential for transmission of these pathogens between animals and their handlers raises important public health concerns. As the first epidemiological study on MRSA surveillance in the FHSU swine unit, stakeholders will be informed on appropriate antibiotic stewardship and biosecurity practices.