| Summary: | 碩士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 94 === The SCCmec types of 382 hospital-acquired methicillin resistant Staphylococcus aureus (HA-MRSA) isolates collected from 1999 to 2005, and 26 community-acquired MRSA (CA-MRSA) isolates recovered in 2005 from northern Taiwan were analyzed retrospectively. Although the majority of HA-MRSA continued to possess SCCmec III in each year throughout the study period, the prevalence of SCCmec type IV in HA-MRSA showed a rapid increase in 2005, reaching 45% after maintaining a fairly steady rate from 3% to 20% from 1999 through 2004. Analysis of randomly selected isolates each year (30 SCCmec type III HA-MRSA, 39 HA-MRSA with SCCmec IV or V and 26 CA-MRSA) by PFGE revealed three major pulsotypes (A, B, and C). Pulsotypes B and C containing SCCmec type IV and V, respectively, were detected not only in CA but also in HA isolates. In the aspect of toxin genes detection, six toxin genes had significantly different distribution in HA-MRSA with SCCmec III and CA-MRSA while there is only one difference between CA- and HA-MRSA carrying SCCmec IV and no difference between CA-and HA-MRSA with SCCmec V. Furthermore, analysis of representative members of the three major pulsotypes by multilocus sequence typing (MLST) revealed that two STs, ST239 and ST59. All SCCmec IV and V MRSA shared the same ST59 genetic background. The more rapid growth rates and better biofilm forming ability may contribute to the spread of SCCmec type IV:ST59 between community and hospital. Therefore, SCCmec type IV, which is usually community-acquired, may become nosocomial in the study.
Besides, in previous study indicated that SCCmec IV cassette of MRSA may be transferred from other coagulase-negative Staphylococcus spp. PFGE, MLST, and mecA down stream were analyzed to realize the relationship of SCCmec cassette between MRSA and MRSE carrying SCCmec IV. The result showed difference in structure between the two species, therefore, the possibility was limited of SCCmec cassette transferred from MRSE to MRSA directly. In addition, variation of resistance to oxacillin was observed in SCCmec IV MRSA and MRSE. The correlation between sequence mutations, RNA level of mecA regulation system, efflux pump and oxacillin MICs was concerned. Only the resistance to oxacillin in MRSE changes while inhibiting the function of efflux pump. As a result, efflux pump played an important role regulating the resistance to oxacillin in MRSE while there would be other factors regulating in MRSA.
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