Molecular epidemiologic characterization of methicillin-resistant Staphylococcus aureus in the northernmost region in Japan: High prevalence of SCCmec-IVa (ST1/spa-t1784) and the emergence of ST22-IVa-PT clone.

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital- and community-associated infections. This study aimed to investigate the molecular epidemiologic characteristics of MRSA in the northernmost region of Japan.

METHODS

Clinical isolates of MRSA were collected from Asahikawa Medical University Hospital, located in Hokkaido, a northernmost region in Japan, for a 14-month period. They were analyzed for their genotypes, virulence factors, and antimicrobial resistance profiles.

RESULTS

Among a total of 235 MRSA isolates collected during the study period, the dominant SCCmec type was IVa (MRSA-IVa, 72%), followed by IIa (26%). MRSA-IVa was assigned to mostly coa genotype VIIa (78%) or IIIa (20%), whereas MRSA-IIa to coa-IIa. ST1/spa-t1784 was the major genotype of coa-VII MRSA-IVa. Panton-Valentine leukocidin (PVL) genes were detected in 11 (4.7%) isolates, among which 10 isolates belonged to CC8 (sequence type [ST]8, ST8455)/spa-t008/agr-I/coa-IIIa, with typical traits of the US300 clone (arginine catabolic mobile element [ACME] type I, sek, seq). One PVL-positive isolate belonged to ST22/spa-t005/agr-I/coa-XIc, harboring the toxic shock syndrome toxin-1 gene (ST22-PT clone). ACME-type II' was identified in PVL-negative ST764/spa-t002/coa-IIa isolates (16% in SCCmec-IIa MRSA).

CONCLUSIONS

Clonal structure of MRSA in the northernmost region of Japan was revealed, suggesting the spread of emerging clones (e.g. ST22-MRSA-PT) to the remote area.