Nasal carriage of Staphylococcus aureus in dogs and owners: Spa typing and antimicrobial resistance in two Italian veterinary hospitals

Staphylococcus aureus is an opportunistic pathogen that colonizes humans and animals and causes a wide range of infections. Within a One Health framework, this study investigated nasal carriage, antimicrobial resistance, and genetic diversity of S. aureus in dogs and their owners attending two Veterinary Teaching Hospitals in Southern and Northern Italy. Strains were characterized using minimum inhibitory concentration testing and spa typing to assess resistance profiles and potential host- or region-associated patterns. A total of 108 S. aureus isolates were recovered from 77 owners and 31 dogs. In 17 dog–owner pairs (6 from Southern Italy and 11 from Northern Italy), S. aureus was isolated from both hosts. Overall, resistance was most frequent to penicillin (72.2%), followed by erythromycin (38%), and cefoxitin and gentamicin (13.9% each). Isolates from Southern Italy showed higher levels of antimicrobial resistance compared to that of Northern Italy. Fifteen isolates (13.9%) were classified as methicillin resistant, and all of which were multidrug resistant. The most common spa type was t1451 in both regions, while other prevalent types differed geographically. Identical spa types were detected in 11/17 dog-owner pairs (64.7%), suggesting possible interspecies transmission or shared environmental sources. No association was observed between spa type and multidrug resistance. These results highlight regional differences in S. aureus populations and confirm the lack of strict host specificity, underlining the importance of integrated One Health surveillance to address zoonotic transmission risks.