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

• MRSA in the northernmost region in Japan were first genetically characterized. • SCC mec -IVa (ST1/ spa -t1784) was dominant clone, surpassing MRSA-IIa (CC5). • ACME-II’ was positive in ST764-MRSA-IIa, in 16% of SCC mec -IIa. • USA300 clone (PVL+/ACME-I+) was identified in 10 isolates (4.2% of MRSA). • ST22-IV-PT (PVL+/TSST-1+) was first identified in the northernmost region in Japan. Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital- and community-associated infections. This study aimed to investigate the molecular epidemiological characteristics of MRSA in the northernmost region of Japan. 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. Among a total of 235 MRSA isolates collected during the study period, the dominant SCC mec type was IVa (MRSA-IVa, 72%), followed by IIa (26%). MRSA-IVa was assigned to mostly coa genotype VIIa (78%) or IIIa (20%), while 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 isolates (4.7%), among which 10 isolates belonged to CC8 (ST8, ST8455)/ spa -t008/ agr -I/ coa -IIIa, with typical traits of the US300 clone (ACME type I, sek, seq ). One PVL-positive isolate belonged to ST22/ spa -t005/ agr -I/ coa -XIc, harboring the TSST-1 gene (ST22-PT clone). ACME-type II’ was identified in PVL-negative ST764/ spa -t002/ coa -IIa isolates (16% in SCC mec -IIa MRSA). 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.