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

1 Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan 2 Department of Dermatology, Takamatsu Red Cross Hospital, 4-1-3 Banchou, Takamatsu, Kagawa 760-0017, Japan 3 Takamatsu Dermatological Research Group, 4-1-3 Banchou, Takamatsu, Kagawa 760-0017, Japan Correspondence Norihisa Noguchi noguchin{at}ps.toyaku.ac.jp Received 24 April 2008 Accepted 1 July 2008 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 β -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 SCC mec types IV or V have spread, particularly in MSSA carrying etb in the community. Abbreviations: CA, community-acquired; ET, exfoliative toxin; MRSA, meticillin-resistant Staphylococcus aureus ; MSSA, meticillin-susceptible Staphylococcus aureus ; SCC, staphylococcal cassette chromosome; SE, staphylococcal enterotoxin.