Clonal change of methicillin-resistant Staphylococcus aureus isolated from patients with impetigo in Kagawa, Japan.

Recently, the USA300 clone, which is a Panton-Valentine leukocidin (PVL)-positive clonal complex 8-staphylococcal cassette chromosome mec type IV (CC8-IV) community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strain, emerged in community and hospital settings in Japan. Hence, clonal types of CA-MRSA strains are predicted to be changing. Nonetheless, long-term surveillance of CA-MRSA has not been conducted in Japan. Here, we investigated the transition and current status of CA-MRSA strains isolated from outpatients with impetigo; the samples were collected between 2007 and 2016 in Kagawa, Japan. The detection rate (22.8%, 488/2139 strains) of MRSA slightly decreased in these 10 years. Molecular epidemiological analyses showed that the prevalence of the CC89-II clone, which is a typical CA-MRSA genotype of causative agents of impetigo, significantly decreased from 48.0% (48/100 strains) in 2007-2009 to 21.9% (16/73 strains) in 2013-2016. By contrast, a non-USA300 CC8-IV clone, which is a highly pathogenic CA-MRSA/J clone, significantly increased in prevalence from 9.0% (9/100 strains) to 32.9% (24/73 strains). The prevalence of PVL-positive CA-MRSA strains increased annually from 2012 (0%) to 2015 (6.7%), whereas only one of these strains turned out to be the USA300 clone. Antibiotic susceptibility data revealed that the rates of resistance to gentamicin and clindamycin among CA-MRSA strains decreased along with the decreased prevalence of the CC89-II clone and increased prevalence of the CA-MRSA/J clone. Our data strongly suggest that the clonal types and antibiotic susceptibility of CA-MRSA isolated from patients with impetigo dramatically changed during the last 10 years in Japan.

Molecular epidemiology and antimicrobial susceptibilities of 273 exfoliative toxin-encoding-gene-positive Staphylococcus aureus isolates from patients with impetigo in Japan.

The molecular epidemiology and antimicrobial susceptibilities of 273 Staphylococcus aureus isolates positive for the exfoliative toxin-encoding gene obtained from patients with impetigo in Japan in 2006 were studied. The mecA gene was detected in 74 meticillin-resistant S. aureus (MRSA) and 23 meticillin-susceptible S. aureus (MSSA) isolates. All isolates with the staphylococcal cassette chromosome (SCC) mec were classified into type IV (92.8%, 90/97) or V (7.2%, 7/97). The ET-encoding gene etb was found primarily in strains with mecA (87.7%, 71/81), whilst eta (86.6%, 161/186) was detected mainly in strains without mecA. The chromosomal enterotoxin-encoding gene cluster egc was found in 83.0% of strains with eta, whilst no enterotoxin-encoding gene was detected in strains with only etb. PFGE showed that each strain carrying eta, etb and etd could be classified into distinct groups. The susceptibility profiles of MRSA to antimicrobial agents excluding beta-lactams were similar to those of MSSA. Gentamicin- and clarithromycin-resistant strains were frequently found for both MRSA and MSSA. The aminoglycoside-resistance gene aacA-aphD was detected in 97.3% of MRSA and 85.4% of MSSA. Additionally, the macrolide-resistance gene ermA or ermC was detected in 67.6% of MRSA and 71.4% of MSSA. Therefore, these results suggest that SCCmec types IV or V have spread, particularly in MSSA carrying etb in the community.