Molecular Epidemiological Characterization of Methicillin-Resistant Staphylococcus aureus from Bloodstream Infections in Northern Japan: Increasing Trend of CC1 and Identification of ST8-SCC mec IVa USA300-Like Isolate Lacking Arginine Catabolic Mobile Element.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major infectious disease pathogen, and its molecular epidemiological profile has been changing. In this study, a total of 279 MRSA isolates were collected from patients with bloodstream infection (BSI) in Hokkaido, northern main island of Japan, for a 2-year period from August 2019 to July 2021. CC5 (ST5/ST764)-MRSA-IIa (SCC mec -IIa) (47%, n  = 132) and CC1 (ST1/ST2725/ST2764)-MRSA-IVa (42%, n  = 116) were found to be major lineages, with CC8-MRSA-IVa being lower prevalence (5%, n  = 13). CC1-MRSA-IVa showed a relatively increased proportion compared with our previous study (22%, 2017-2019). Seven isolates with SCC mec IVa (2.5%) were positive for Panton-Valentine leukocidin genes on ΦSa2usa and belonged to ST8/ spa -t008/ agr -I/ coa -IIIa, showing genetic features of the USA300 clone. Among these isolates, six isolates harbored arginine catabolic mobile element (ACME) type I typical to the USA300 clone, while it was not detected in an isolate (strain R3-8). Whole genomic analysis of strain R3-8 revealed that its chromosome was highly similar to the USA300 strain TCH1516, but lacked ACME, carrying a plasmid genetically close to that of USA300 strains. The present study revealed increasing trend of CC1-MRSA-IV and occurrence of a novel variant of the USA300 clone among MRSA from BSI in northern Japan.