Characterization of fusidic acid-resistant Staphylococcus aureus isolated from food animals during 2010-2021 in South Korea

Livestock-associated fusidic acid-resistant Staphylococcus aureus (FRSA) is frequently linked to global public health hazards. This study aimed to ascertain the prevalence and molecular characteristics of FRSA isolated from food animal products in South Korea from 2010 to 2021. We obtained a total of 3980 S. aureus isolates from cattle carcasses (n = 482), pig carcasses (n = 1531), and chicken carcasses (n = 1967). The isolates were evaluated for antimicrobial susceptibility using the broth microdilution method. Antimicrobial resistance genes, spa types, sequence types (STs), and Staphylococcus cassette chromosome mec (SCCmec) types were determined by polymerase chain reaction (PCR) and sequencing analysis. In total, 187 isolates (4.7 %) demonstrated resistance to fusidic acid, with the maximum recovered from cattle (16.2 %), followed by pigs (6.5 %) and chickens (0.5 %). In addition, the majority of the isolates showed resistance to penicillin (86.6 %), while comparatively low resistance rates (7-13.9 %) were observed for erythromycin, gentamicin, kanamycin, and tetracycline. Moreover, multidrug resistance (MDR) comprised 8.6 % (16/187) of the isolates. Among the fusidic acid resistance determinants, the fusA mutation was the highest, containing 54 % (101/187), followed by fusC (29.4 %, 55/187) and fusB (15.5 %, 29/187). A high level of resistance regarding the substitution of L461K in the fusA gene was identified in 97 % of isolates. In addition, the most commonly detected resistance patterns include penicillin (87.1 %, 88/101) among the FRSA. The nucleotide sequencing analysis showed that all 29 fusB-carrying isolates possess the structural gene blaZ of the bla operon and the insertion sequences orf152, orf170, IS257, and orf152. In total, 21 spa types were found, where t126 was detected the most (81.2 %, 82/101) in fusA, followed by t127 (81.8 %, 45/55) in fusC, and t189 (27.6 %, 8/29) in fusB. Furthermore, all t002 harboring fusC were detected as ST5-MRSA-SCCmecII clones. This is the first report of fusA and fusB carrying S. aureus and linkage fusB and blaZ genes in FRSA isolated from food animal products. Taken together, the FRSA in food animals with different resistance determinants and spa types could pose a threat to public health.