Infectious Dermatitis in Companion Animals: A One Health Perspective.

Infectious dermatitis is a common condition in companion animals and is frequently associated with opportunistic bacterial pathogens, particularly staphylococci. The emergence of antimicrobial resistance among these pathogens represents a growing challenge for veterinary medicine and public health. This study aimed to assess the presence of Staphylococcus species, dermatophytes, and ectoparasites in companion animals presenting clinical signs of dermatitis in Northern Portugal, and to characterize the antimicrobial resistance profiles of the isolated staphylococci. A total of 58 infectious dermatitis cases yielded 71 dermatological samples from dogs and cats between September 2025 and January 2026. Staphylococcus isolates were identified by MALDI-TOF MS and analyzed for phenotypic antimicrobial susceptibility and resistance genes by PCR. Twenty-nine Staphylococcus isolates were identified, with S. pseudintermedius being the predominant species (66%). Resistance to at least one antimicrobial agent was observed in 65% of isolates, while multidrug resistance was detected in 7%. The highest resistance rates were observed for penicillin (62%), tetracycline (24%), and oxacillin (21%). The most prevalent resistance genes were tetM (86%), blaZ (86%), and mecC (83%). No dermatophytes were detected, and two ectoparasite-positive (Demodex spp. and Otodectes spp.) cases were identified. These findings highlight the presence of antibiotic-resistant S. pseudintermedius in companion animal dermatitis and reinforce the importance of early antimicrobial susceptibility testing and continuous surveillance of antimicrobial resistance in veterinary dermatology.