Antimicrobial resistance in Staphylococcus pseudintermedius isolated from asymptomatic and symptomatic dogs in Montevideo, Uruguay: characterization of MRSP strains and genetic determinants of resistance.

Staphylococcus pseudintermedius is a common opportunistic pathogen in dogs and an increasing concern in veterinary medicine due to rising antimicrobial resistance, particularly to methicillin. This study aimed to characterize resistance profiles and genetic mechanisms in isolates from healthy and diseased dogs in Montevideo, Uruguay. A total of 133 isolates was analyzed (83 from clinical infections and 50 from asymptomatic carriers). Antimicrobial susceptibility was assessed by disk diffusion following veterinary guidelines. Resistance genes and SCCmec types were detected by PCR. Ten representative isolates underwent whole genome sequencing. High resistance rates were observed for penicillin (81%), erythromycin (49.6%), and clindamycin (45%). Overall, 48.9% of isolates were multidrug-resistant. Phenotypic resistance to oxacillin was detected in 26% of isolates; however, 23% carried mecA gene and were therefore classified as genotypic MRSP. These isolates were more frequent among dogs with clinical infections. These strains showed higher resistance to all antimicrobials tested. SCCmec type V was the most prevalent, and greater genetic diversity was found among isolates from symptomatic dogs. Genomic analysis revealed circulating strains of unassigned sequence types (STs), a variety of resistance genes within specific lineages, the circulation of SCCmec XIV cassette carrying strains, and an Oxacillin-susceptible Methicillin-resistant Staphylococcus pseudintermedius (OS-MRSP) isolate. These findings demonstrate the clinical and epidemiological relevance of S. pseudintermedius in Uruguay and the role of asymptomatic dogs as reservoirs of resistant strains. The results emphasize the need for surveillance, prudent antimicrobial use, and integrated control strategies within a One Health framework.