Comparative assessment of genotypic and phenotypic correlates of Staphylococcus pseudintermedius strains isolated from dogs with otitis externa and healthy dogs.

Staphylococcus pseudintermedius is considered a primary pathogen of canine skin and soft tissue infections, and the rapid emergence of methicillin-resistant S. pseudintermedius worldwide is a major issue. In the current study, genotypic and phenotypic correlates associated with S. pseudintermedius causing canine otitis externa were evaluated using 41 S. pseudintermedius strains isolated from dogs with otitis externa (n = 26) and healthy dogs (n = 15). The S. pseudintermedius strains were subjected to a comparative analysis of (i) genotypes (multilocus sequence typing, agr, and spa types), (ii) methicillin resistance and SCCmec types, (iii) multidrug resistance (MDR), (iv) biofilm formation, and (v) susceptibility to canine cathelicidin (K9CATH). A high degree of genetic diversity was observed in both groups of S. pseudintermedius strains, regardless of methicillin resistance. Almost all methicillin-resistant strains (>95%) harbored SCCmec V and displayed MDR. Although there was no difference in biofilm formation, S. pseudintermedius strains derived from otitis externa exhibited enhanced resistance to cationic antimicrobial peptide (K9CATH) compared with strains from healthy dogs. The high degree of heterogeneity in MLST, agr, and spa types prevented the identification of correlations between any specific genotype and virulence phenotype in otitis externa caused by S. pseudintermedius, These findings provide an important basis for monitoring and treating canine skin and soft tissue infections in Korea.