Integration analysis of pSK41 in the chromosome of a methicillin-resistant Staphylococcus aureus K-1.

An integrate of pUB110 carrying aadD and blmS genes conferring resistance to 4'-OH containing aminoglycosides and bleomycin, respectively, is found in the Staphylococcal conjugative plasmid pSK41 and in the mec chromosomal region. In this study, we found an integrated copy of pSK41 in the chromosome of an arbekacin-resistant MRSA strain, K-1, clinically isolated in Japan. This is the first report of the chromosomal integration of this large plasmid in MRSA. Analysis of the nucleotide sequence and restriction map revealed a complete homology of the blmS-containing region of the integrate to wild type pSK41, except for the deletion of aadD and a part of the repU gene. In addition, we have discovered an insertion of IS1182 within the pSK41 integrate. Pulse-field gel electrophoresis-Southern analysis showed that the integration occurred outside the mec region. We also found that deletion of aadD resulted in an aberration of blmS transcription.