Genomics and post-genomics of Staphylococcus aureus causing bullous impetigo

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In this study, we collected bacterial specimens by seed swab from lesions of bullous impetigo patients with the cooperation of more than 60 nation-wide hospitals and open clinics in Japan and isolated Staphylococcus aureus in our laboratory. We identified 1,017 S.aureus strains. The isolated strains were subjected to PFGE by SmaI digestion, Southern hybridization for genes of eta,etb,etd, coagulase testing, agglutination test for SEA,SEB,SEC,SED,PCR testing for eta,etb, etd,sea, seb,sec,sed,tsst-1,femA,mecA. The overaII PFGE patterns of isolated strains weresubjected to clustering analysis by Gel Compar. Isolated strains were also subjected for measurement of MIC against cefem, macrolide, fusigic acid, tetracycline, quinolone. Upon these characterization, we discovered that strains causing bullous impetigo in Japan were clustered in five clonal groups and their producibility of exfoliative toxin, coagulase types well correlated with clustering results, i.e.there are three ETA-producing clusters, one ETB-producing and one ETD-producing clusters. Three ETA-producing clusters are coagulase type V,III, and VII respectively. ETB-producing cluster is type I and ETD-producing cluster is type II. Surprisingly, 100% of coagulase type III ETA-producing cluster is mecA positive and 70% of ETB-producing cluster is mecA positive. Multilocus sequencing results well correlated with clustering analysis indicating their clonality. MIC testing clearly indicated that those mecA positive strains are borderline level resistant to β-lactams. These results strongly suggested that in Japan now teo clonal groups causing bullous impetigo are expanding as MRSA.