Characterization of a community-acquired methicillin-resistant sequence type 338 Staphylococcus aureus strain containing a staphylococcal cassette chromosome mec type VT

Objectives: To determine the molecular characteristics of a sequence type 338 community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strain and the relationship among MRSA strains from various lineages and areas. Methods: Whole-genome sequencing, genomic comparison, antimicrobial susceptibility testing, and hemolysis analysis were performed to identify the resistance determinants and virulence factors of strain ZY05 and the relationships among CC59 clones. Results: MRSA strain ZY05 was resistant to tetracycline, erythromycin, and clindamycin, and the resistance genes erm(B) and tet(K) were detected in the genome. ZY05 harbors the genomic islands νSaα, νSaβ, νSaγ, and ΦSa2, the pathogenicity island νSa1, and virulence factors such as Panton–Valentine leukocidin, phenol-soluble modulins, alpha-hemolysin, enterotoxin B, enterotoxin K, and enterotoxin Q, which are the same as those present in ST59 strains. In addition, the virulence potential of ST338 did not differ from that of ST59. This strain contains the staphylococcal cassette chromosome mec (SCCmec) type VT, a distinct SCCmec type previously reported from Taiwan. The results of core genome multilocus sequence typing (cgMLST) analysis showed that the gene distances between ST59 and ST338 were close among CC59 isolates, while strains from Taiwan were identical to isolates from the Chinese mainland with respect to these two sequence types. Conclusions: The ST338 strain ZY05, which has a close genetic relationship to ST59 strains, is multidrug-resistant and highly virulent. Strains of two identical lineages, ST59 and ST338, from Taiwan and the Chinese mainland may have the same genetic background. Keywords: CA-MRSA, ST338, ST59, Whole-genome sequencing, China