Acquisition of methicillin resistance and progression of multiantibiotic resistance in methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) produces specific penicillin-binding protein, PBP2', which shows remarkably low affinities to most beta-lactam antibiotics except those such as penicillin G and ampicillin. The region surrounding mecA has been called additional DNA or mec and is thought to be of extraspecies origin. From the study of mec, we found that mec is a novel mobile genetic element and designated as staphylococcal cassette chromosome mec (SCCmec). There are three types of SCCmec. In the past decades, MRSA has become resistant to many antibiotics, such as carbapenems, new quinolones, and minocycline etc. It seems to be a characteristic of MRSA to acquire multi-resistance by accumulating multiple resistance genes around the mecA gene inside SCCmec.