Species Diversity and Antimicrobial Susceptibility of Staphylococci Colonising Healthy Dogs—A Single-Centre Cross-Sectional Study in Bulgaria

Background/Objectives: Dogs are important carriers and transmitters of staphylococci from surface microbiota. Carriage screening allows for the identification of animals colonised with pathogens such as methicillin-resistant S. pseudintermedius (MRSP) and methicillin-resistant S. aureus (MRSA), which are spread between animals and from dogs to humans. This cross-sectional study determined the diversity of staphylococci from the surface microbiota of clinically healthy dogs in Bulgaria and their susceptibility to antimicrobial agents. Methods: The study was performed with 30 healthy dogs reared in the region of Stara Zagora, Bulgaria in 2024 and 2025. Swabs were obtained from eight body sites from each dog and incubated on blood and mannitol salt agar. Random isolates were identified by MALDI-TOF MS and tested for resistance to oxacillin/cefoxitin and to 14 classes of antimicrobial drugs (AMD). Results: Ninety out of 100 tested isolates were confirmed as Staphylococcus spp. from 15 different species. The total share of coagulase-positive (CoPS) staphylococci significantly exceeded that of coagulase-negative (CoNS) ones. Fifteen phenotypically methicillin-resistant staphylococci were identified—eight CoNS and seven CoPS—and confirmed by MIC test. The highest resistance was against penicillin (64.4%), ampicillin and minocycline (52.2%), whereas the highest sensitivity was to rifampin, amikacin, cefquinome and amoxicillin + clavulanic acid. Conclusions: Data about the carriage of MRSP, MRSA and multidrug-resistant coagulase-negative staphylococci in healthy dogs are important in view of the increased risk of colonisation/infection for people in contact with these dogs in households and veterinary facilities (clinics, hospitals). This supports the “One Health” approach integrating animal, human and environmental health.