| Summary: | 碩士 === 國立臺灣大學 === 醫事技術學研究所 === 90 === Staphylococcus aureus is recognized as one of the most important bacterial pathogens seriously contributing to the problem of hospital infections all over the world. Methcillin-resistant S. aureus (MRSA) has been a serious problem since 1980s in Taiwan. The resistance of methicillin is mostly due to an additional large DNA cassette (designated the staphylococcal cassette chromosome mec [ SCCmec ] ) inserted in the chromosome. The mecA gene encoding PBP2a is a component of this large fragment, SCCmec. Two major types of resistance have been observed, heterogeneously or homogeneously phenotypic expression. Expression of PBP2a is considered to be controlled regulator elements that are putative transmembrane- signalling protein and repressor protein encoded by mecR1 and mecI genes. The expression of these regulators represses mecA transcription in the absence of inducer. Deletion or mutation that occurred in mec regulator gene is considered to be associated with constitutive production of PBP2a. However, regulator elements other than mecI and mecR1 also are reguired for strong repression of PBP2a. Correlation of resistance phenotype and mecA upstream and downstream region polymorphism were analyzed in this study. The distribution of mec regulator genes was analyzed by PCR-RFLP and sequencing. For the polymorphism of downstream region the MRSA isolated were analyzed by ClaⅠ-digested hybridization patterns with mecA gene as the probe. In addition, the mRNA expression level of mecA was observed among strains with various degree of resistance(oxacillin MIC,4~256μg/ml). The results revealed that the presence or absence of mecR1, was correlated with levels of resistance. Molecular typing of MRSA isolated by RAPD and PFGE showed that the clonal spread was also possible for high-level resistant MRSA isolates.
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