Prevalence and antimicrobial susceptibility of Staphylococcus aureus isolated from dairy goats in Shaanxi, China, with genomic characterization of a multidrug-resistant subset.

Abstract

Staphylococcus aureus (S. aureus) is a major etiological agent of mastitis in dairy goats and a potential reservoir of antimicrobial resistance (AMR). In the present study, the prevalence and antimicrobial susceptibility of S. aureus isolated from goat milk in Shaanxi Province, China, was investigated and the genomic features of a multidrug-resistant (MDR) subset were characterized. A total of 184 (10.7%) S. aureus isolates were recovered from 1720 milk samples collected from 19 dairy farms. Antimicrobial susceptibility testing against 18 agents showed that the isolates exhibited an overall favorable susceptibility profile, with resistance remaining uncommon for most drugs tested. However, nine isolates (4.9%) were classified as MDR, including three (1.6%) methicillin-resistant S. aureus (MRSA) isolates. Although MDR was uncommon in the sample, genomic analysis showed that the MDR subset comprised a limited number of high-risk lineages, including MRSA ST59 and methicillin-susceptible S. aureus (MSSA) ST398. Comparative phylogenetic analysis indicated that the MRSA ST59 and MSSA ST398 isolates were genetically related to publicly available human and porcine-associated genomes, respectively, consistent with possible host spillover. In addition, the MSSA ST398 and ST522 isolates contained putative host-associated virulence factor variants that warrant further functional validation. Overall, the present study provides region-specific surveillance data on milk-associated S. aureus in dairy goats and highlights the importance of continued integrated surveillance of high-risk S. aureus lineages within the One Health framework.