High Prevalence of Methicillin- and Multidrug-Resistant Golden Staphylococci in Nasal Carriage of Companion Dogs in South Region of Espírito Santo, Brazil: Implications for One Health Surveillance

Abstract

Aims: This study aimed to determine the prevalence and antimicrobial resistance profiles of golden-pigmented staphylococci isolated from the nasal mucosa of dogs that visited at a veterinary clinic in Bom Jesus do Norte, Espírito Santo, Brazil, in 2024, considering zoonotic implications and the One Health paradigm. Study design: The study employed a cross-sectional, descriptive, retrospective, and observational design, involving microbiological data collection and antimicrobial susceptibility testing. Place and Duration of Study: The research was conducted with dogs attending a veterinary clinic in Bom Jesus do Norte, southern Espírito Santo, Brazil. Sample collection occurred between February and December 2024. Methodology: The sample comprised 72 healthy dogs that had not received antimicrobials in the six months prior to sampling and whose owners provided informed consent. Nasal swabs were collected and inoculated onto mannitol salt agar and sheep blood agar. Following isolation of golden-pigmented colonies, phenotypic identification was performed using Gram staining, catalase, coagulase, DNase, hemolysis on blood agar, and mannitol fermentation tests. Antimicrobial susceptibility testing was carried out via the Kirby-Bauer disk diffusion method, following EUCAST guidelines. Fifteen antibiotics from different classes were tested. Results: The prevalence of golden-pigmented staphylococci was 31.9% (23/72). Universal resistance to natural penicillins (penicillin and ampicillin) was observed. Resistance to cefoxitin, a phenotypic marker for methicillin resistance, was 60.9%, with an additional 30.4% of isolates classified as intermediate, yielding a total of 91.3% potentially methicillin-resistant strains when both categories were combined. Oxacillin showed only 13.0% resistance or intermediate results, underscoring its inadequacy as a standalone marker for methicillin resistance. Most isolates were susceptible to linezolid, rifampicin, Tetracycline, and gentamicin. One isolate was resistant to vancomycin, and another exhibited intermediate susceptibility. The multidrug resistance rate (resistance to ≥3 antibiotic classes) was 47.8% (11/23). Resistance profiles differed significantly from prior Brazilian studies, showing higher resistance to beta-lactams and lower resistance to sulfamethoxazole-trimethoprim and ciprofloxacin. Conclusion: The high prevalence of methicillin-resistant and multidrug-resistant golden staphylococci in apparently healthy dogs indicates that these animals serve as community reservoirs of antimicrobial resistance. These findings reinforce the need for rational antimicrobial use in both human and veterinary medicine, continuous surveillance, and implementation of biosafety practices—particularly in settings of close human–animal interaction. The detection of vancomycin-resistant strains—an antibiotic not used in veterinary medicine—suggests possible reverse zoonotic transmission or horizontal gene transfer from human strains, highlighting the interdependence of human, animal, and environmental health. Addressing this issue through the One Health lens is essential to mitigate the risks associated with the dissemination of resistant strains.