Methicillin-Resistant Clonal Complex 398 as a Major MRSA Lineage in Dogs and Cats in Thailand.

The aim of this study was to present molecular and antimicrobial resistance characteristics of methicillin-resistant (MRSA) clonal complex (CC) 398 isolated from diseased dogs and cats in Thailand. A total of 20 MRSA isolates of 134 isolated from canine and feline clinical samples during 2017-2020 were CC398, consisting of sequence type (ST) 398 (18 isolates), ST5926 (1 isolate), and ST6563 (1 isolate) by multilocus sequence typing. t034 and staphylococcal cassette chromosome (SCC) V were predominantly associated with ST398. Intraclonal differentiation was present by additional (t1255, t4653), non-detectable , composite SCC with a hybrid of + and class A complex, and DNA fingerprints by pulsed-field gel electrophoresis. The isolates essentially carried antimicrobial resistance genes, mediating multiple resistance to β-lactams (, ), tetracyclines [(M)], aminoglycosides [], and trimethoprim (). Livestock-associated MRSA ST398 resistance genes including (B), (E), , , and (L) were heterogeneously found and lost in subpopulation, with the absence or presence of additional (A), (B), and genes that corresponded to resistance phenotypes. As only a single CC398 was detected with the presence of intraclonal variation, CC398 seems to be the successful MRSA clone colonizing in small animals as a pet-associated MRSA in Thailand.