Clonal Complexes and Antimicrobial Susceptibility Profiles of Staphylococcus pseudintermedius Isolates from Dogs in the United States

Staphylococcus pseudintermedius is the primary cause of canine pyoderma and has been associated with diseases in other animals, including human beings. A high prevalence of methicillin and multidrug resistance has been reported in this bacterium in some geographic regions of the United States. Multilocus sequence type (MLST) 68 was implicated, initially, as the major clonal genotype based on a limited number of samples. The objectives of this study were to determine the population genetics of S. pseudintermedius isolated from a cross-section of the United States using a seven-locus multilocus sequence typing method, to identify clonal complexes (CCs), and to correlate sequence types with antimicrobial susceptibility profiles. A total of 190 S. pseudintermedius with 86 different MLSTs were detected and the constituents of three major CCs of methicillin-resistant S. pseudintermedius (MRSP), CC68, CC71, and CC84, were identified. Different patterns of resistance were associated with each CC. CC71 from the United States had notable differences with CC71 studied on other continents with chloramphenicol, tetracycline, and trimethoprim/sulfamethoxazole resistance. Some isolates with resistance to the broadest range of drugs tested, including that to chloramphenicol, had STs unrelated to the major CCs, suggesting the potential for the emergence of new clonal populations of MRSP that are resistant to most therapeutically useful antimicrobials.