Antimicrobial Susceptibility Patterns and Resistance Accumulation in Oral Bacterial Isolates from Domestic Dogs in Southern Ecuador

This study characterized the cultivable oral microbiota of domestic dogs and evaluated antimicrobial susceptibility patterns and resistance accumulation in a veterinary context. A cross-sectional analytical design was conducted including 100 domestic dogs attended in urban veterinary clinics in southern Ecuador, from which 139 bacterial isolates were obtained through oral swabbing and conventional microbiological identification. Antimicrobial susceptibility was assessed using the disk diffusion method according to CLSI guidelines. Resistance accumulation was defined as the number of antimicrobial classes to which each isolate exhibited resistance, and multidrug resistance as resistance to three or more classes. A predominance of Gram-negative bacteria was observed (65.5%), with Pseudomonas (27.3%), Klebsiella (20.9%), and Enterobacter (7.9%) as the most frequent genera, while Staphylococcus aureus represented 34.5% of isolates. Resistance to at least one antimicrobial was detected in 71.2% of isolates, and multidrug resistance in 9.4% of the total dataset, exclusively among Gram-negative bacteria, corresponding to 14.3% within this group. Resistance to two or more antimicrobial classes was observed in 42.9% of Gram-negative isolates. Multivariable logistic regression showed that bacterial genus was the only factor significantly associated with resistance accumulation, with Enterobacter presenting a higher odds ratio compared to Pseudomonas (adjusted OR = 16.30; 95% CI: 1.69–157.14; p = 0.016), while host-related variables were not significant (p > 0.05). These results indicate that antimicrobial resistance in the canine oral microbiota is primarily structured by bacterial identity rather than host factors, highlighting the role of the oral cavity as a reservoir of resistant bacteria with implications for veterinary clinical practice and epidemiological surveillance.