Staphylococcus pseudintermedius is a frequent opportunistic pathogen in dogs and an emerging concern in veterinary medicine because of increasing antimicrobial resistance, particularly to methicillin. The organism has zoonotic potential and can circulate between animals and humans, making its resistance patterns and genetic determinants relevant for clinical management and public health. This study characterized resistance phenotypes and genetic determinants in isolates from both symptomatic and asymptomatic dogs in Montevideo, Uruguay.
A total of 133 S. pseudintermedius isolates were analyzed: 83 obtained from clinical infections and 50 from asymptomatic canine carriers. Antimicrobial susceptibility testing was performed by disk diffusion following veterinary standards. Detection of resistance genes and characterization of staphylococcal cassette chromosome mec (SCCmec) types were carried out by PCR. Ten representative isolates were subjected to whole genome sequencing to further resolve sequence types (STs), resistance gene content, and SCCmec variants.
High levels of phenotypic resistance were documented for several commonly used agents. Resistance rates reported in the study included penicillin at 81%, erythromycin at 49.6%, and clindamycin at 45%. Nearly half of the isolates, 48.9%, were classified as multidrug-resistant. Isolates classified as resistant by phenotype tended to show broader resistance profiles compared with susceptible isolates. These findings highlight substantial resistance burdens among S. pseudintermedius isolates sampled in this setting.
Phenotypic resistance to oxacillin was observed in 26% of isolates. Genotypic testing identified the mecA gene in 23% of isolates, which were therefore classified as genotypic MRSP (methicillin-resistant S. pseudintermedius). MRSP isolates were more frequently recovered from dogs with clinical infections than from asymptomatic carriers and demonstrated higher resistance rates across the panel of antimicrobials tested. The study also reported at least one Oxacillin-susceptible Methicillin-resistant S. pseudintermedius (OS-MRSP) isolate identified through genomic analysis, underscoring the potential discordance between phenotype and genotype in some cases.
Among detected cassettes, SCCmec type V was the most prevalent in this collection. Whole genome sequencing of ten representative isolates revealed additional complexity: circulation of strains carrying the SCCmec XIV cassette, the presence of isolates that could not be assigned to known sequence types (unassigned STs), and lineage-associated arrays of resistance genes. The study found greater genetic diversity among isolates from symptomatic dogs compared with those from asymptomatic carriers, suggesting a wider range of circulating lineages in clinical infections. The genomic data therefore documented both known and less-characterized MRSP genetic elements within the local population.
The results demonstrate that S. pseudintermedius in Montevideo exhibits high levels of resistance to several antimicrobials and a substantial proportion of mecA-positive MRSP. MRSP isolates were associated with clinical disease and broader resistance profiles. Importantly, asymptomatic dogs also harbored resistant strains, indicating that healthy carriers can act as reservoirs for dissemination. The study authors emphasize the need for continued surveillance, implementation of antimicrobial stewardship in veterinary practice, and integrated control measures that align with a One Health perspective to limit spread between animals and humans and to preserve therapeutic options.
This study characterizes antimicrobial resistance patterns and genetic determinants of S. pseudintermedius from dogs in Montevideo, Uruguay. Key findings include high penicillin resistance (81%), substantial erythromycin and clindamycin resistance (49.6% and 45%, respectively), a 48.9% multidrug-resistance rate, phenotypic oxacillin resistance in 26% of isolates, and mecA carriage in 23% (genotypic MRSP). SCCmec type V was most common; genomic analyses revealed unassigned STs, SCCmec XIV–carrying strains, and an OS-MRSP isolate. Asymptomatic carriers contribute to the reservoir of resistant strains.
Based on the findings reported, the study underscores the need for targeted surveillance of S. pseudintermedius, judicious antimicrobial prescribing in veterinary medicine, and integrated One Health strategies to monitor and mitigate the spread of resistant and methicillin-resistant strains. Details on sampling periods, geographic distribution within Montevideo, and specific sequence type assignments beyond those described by the authors were not reported in the abstract.