[Mechanisms of methicillin and vancomycin resistance in Staphylococcus aureus]

Abstract

The mechanism of methicillin and vancomycin resistance in Staphylococcus aureus (MRSA) is discussed, focusing on the phenotypic expression of resistance; i.e., pre-methicillin resistance, Egle-type resistance, heterogeneous and homogeneous resistance. Acquisition of staphylococcus cassette chromosome(SCCmec) by a recipient MSSA strain in the mecA-positive, and methicillin-susceptible status(pre-MRSA status) of S. aureus. Subsequent of the mecI-gene-mediated repression of mecA gene transcription results in the heterogeneous expression of methicillin resistance. It is only with the alternation of another chromosomal locus that the heterogeneous-to-homogeneous (hetero-to-homo) conversion of methicillin resistance occurs. Acquisition of a part of vancomycin-resistance(the level of hetero-VRSA) is associated with hetero-to-homo conversion of methicillin resistance, and full expression of vancomycin resistance(MIC = 8 mg/l) is achieved by additional acceleration of cell-wall synthesis causing apparent cell-wall thickening.