Purpose: This study aims to understand the susceptibilities of CoNS to non-β-lactam antimicrobials and identify the resistance determinants.
Methods: A total of 87 CoNS recovered from food animals were characterized by antimicrobial susceptibility testing, resistance gene identification, and conjugation tests.
Results: Of 7 staphylococcal species studied, S. lentus, S. sciuri, S. xylosus, and S. haemolyticus, accounted for over 96% of the isolates. In addition to β-lactam resistance, high percentages of CoNS were resistant to tetracycline (67.8%), erythromycin (36.7%), clindamycin (27.5%), and quinopristin/dalfopristin (14.9%). A total of 47 isolates (54%) were resistant to at least 3 antimicrobial classes, including 6 CoNS resistant to 6 antimicrobial classes. The common genes for the above mentioned resistance phenotypes were mec(A), tet(M), erm(A), and vga(A), which were identified from 68.7%, 61%, 56.2%, and 69.2% of the isolates, respectively. tet(M) was conjugatively transferable from 11 tetracycline-resistant CoNS to a Enterococcus strain, underlining the potential of antimicrobial resistance transfer from Staphylococcus to the commensal bacteria in human.
Significance: This study suggests that multidrug resistance is common in CoNS in animals and adds to our knowledge of the potential of CoNS serving as antimicrobial resistance donors in the food production environment.