Nasal Colonization of Antimicrobial‐Resistant and Biofilm‐Producing Staphylococcus spp. in Surgical Canine Patients From Italy

Background: Staphylococcus spp. commonly colonise the skin and mucosal surfaces of dogs and may act as opportunistic pathogens under favourable conditions. Antimicrobial resistance and biofilm formation are key traits that may contribute to bacterial persistence and reduced susceptibility to antimicrobial agents. Objectives: This study aimed to characterise the antimicrobial resistance profiles and biofilm-forming ability of Staphylococcus spp. isolated from the nasal cavities of dogs admitted to the Surgical Unit of the Veterinary Teaching Hospital in Naples, Italy. Methods: Nasal swabs were collected from 100 dogs prior to surgery. Strains were identified by MALDI-TOF mass spectrometry. Antimicrobial susceptibility testing was performed using the disk diffusion method according to international guidelines. Biofilm formation was assessed using a quantitative crystal violet assay. Results and Conclusions: A total of 65 Staphylococcus strains were recovered. Staphylococcus pseudintermedius was the most prevalent species (40%; χ2 = 134.6, df = 14, p < 0.001), followed by Staphylococcus aureus (15.4%) and Staphylococcus epidermidis (7.7%). High levels of resistance were observed to several antimicrobials, with 61.5% and 4.6% of strains being classified as multidrug-resistant (MDR) and extensively drug-resistant (XDR), respectively. Notably, all tested isolates exhibited biofilm formation, with the majority (56.9%) classified as moderate producers. These findings highlight the presence of antimicrobial-resistant and biofilm-forming Staphylococcus spp. in the nasal cavities of dogs undergoing surgery. The coexistence of these traits may contribute to bacterial persistence, representing a concern for clinical management. Therefore, preoperative nasal screening in high-risk patients should be considered to optimize prophylactic antimicrobial protocols and reinforce infection control in veterinary surgical settings.