[Genetics of multiresistant MRSA].

Since the introduction of methicillin, methicillin resistant S. aureus (MRSA) was appeared in 1961 in England. MRSA produces specific penicillin-binding protein PBP2' which shows very low affinity to most of beta-lactam antibiotics. The region around mecA is called additional DNA or mec DNA and is thought to be extraspecies origin. From the study of mec DNA, it was revealed that there were three types of mec DNA. In the case of mec DNA of N315, a transposon Tn554 which encoded erythromysin and spectinomycin resistance, and a plasmid pUB110 which encoded resistance to kanamycin, tobramycin, and bleomycin were integrated. MRSA became resistant to many antibiotics during a few years which were effective at the time of introduction, such as, carbapenems, new quinolones, and minocycline. MRSA has changed their properties by obtaining resistance-genes or generating mutations on its chromosomal DNA.