Significant increase in the prevalence of Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus, particularly the USA300 variant ΨUSA300, in the Japanese community

USA300, a major Panton-Valentine leukocidin (PVL)-producing methicillin-resistant Staphylococcus aureus (MRSA) clone associated with skin and soft tissue infections (SSTIs), carries a type IV staphylococcal cassette chromosome mec (SCCmec) element. Recently, a USA300 variant, psi USA300, with a 12-bp deletion of ccrB2 in the SCCmec element, was identified in Japan by Takadama et al. (15). To understand the current status of PVL-positive MRSA in the community, a nationwide surveillance of MRSA isolated from outpatients at dermatology departments was conducted. This study included 1,619 outpatients who visited dermatology departments at 22 healthcare facilities in 11 prefectures in Japan between 2018 and 2021; S. aureus were isolated from these outpatients. Molecular epidemiological analysis was performed using PCR, SCCmec and spa typing, pulsed-field gel electrophoresis, multilocus sequence typing, and antimicrobial susceptibility testing. A total of 980 S. aureus were isolated, 293 of which were identified as MRSA. Among MRSA isolates, PVL genes were detected in 18 of 63 (28.6%) in 2018, 34 of 85 (40.0%) in 2019, 29 of 65 (44.6%) in 2020, and 40 in 80 (50.0%) in 2021. Among the PVL-positive MRSA, 16 of 121 (13.2%) and 94 of 121 (77.7%) isolates were identified as USA300 and psi USA300, respectively. psi USA300 strains were collected from six prefectures in Japan: Kagawa, Osaka, Tokyo, Kanagawa, Fukushima, and Saitama. psi USA300 was isolated more frequently than USA300 from patients with deep-seated SSTIs (P < 0.05). Our findings showed that PVL-positive MRSA isolates were significantly increased in the Japanese community. Furthermore, the USA300 variant psi USA300 has emerged as the predominant PVL-positive MRSA clone across the Kanto, Kinki, and Shikoku regions of Japan, and this variant may possess a greater propensity to cause deep-seated SSTIs than in USA300.