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Title: | 抗methicillin葡萄球菌之分子流行病學和抗藥基因分析 Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus and Staphylococcus epidermidis and Characterization of Resistance Genes |
Authors: | Yu-Hsuan Huang 黃聿玄 |
Advisor: | 鄧麗珍(Lee-Jene Teng) |
Keyword: | 金黃色葡萄球菌,分子流行病學,抗藥基因, methicillin-resistant Staphylococcus aureus,SCCmec, |
Publication Year : | 2006 |
Degree: | 碩士 |
Abstract: | Methicillin-resistant Staphylococcus aureus (MRSA) 是造成院內感染的重要致病菌, 一般而言帶有危險因子(如:長期住院、移植人工瓣膜、手術等…)的病人較容易受到感染, 這類的感染通稱為Hospital-acquired MRSA (HA-MRSA) infection, 但近幾年發現在健康的人也有受到MRSA感染的情形發生, 稱之為Community- acquired MRSA (CA-MRSA) 感染。 而在先前的研究中發現HA-MRSA主要以第三型SCCmec為主, 而CA-MRSA大都為第四或第五型SCCmec, 因此本次實驗隨機收集了382株HA-MRSA (1999年到2005年) 和26株CA-MRSA (2005年), 進行SCCmec的分析, 發現HA-MRSA仍以第三型的為主, 而CA-MRSA則是第四或第五型。 但值得注意的是第四型SCCmec在HA-MRSA的分布有增多的趨勢, 因此將菌株分為HA-MRSA (SCCmec III)、HA-MRSA (SCCmec IV or V)、CA-MRSA三大群討論, 分別針對病人基本資料、毒力因子、抗藥型態、基因背景等進行分析, 結果發現菌株含三個主要的clone (A, B, C), 分別屬於SCCmec III, IV, V, 彼此間的差異甚大, 特別的是clone B和C同時傳播於醫院和社區間。 另外針對SCCmec第四型在醫院分布增多的現象做了進一步的討論, 發現快速的生長和更強的形成biofilm的能力可能提供了生長的優勢, 使之適合在醫院內傳播。
此外, 根據先前的研究推測MRSA SCCmec IV的cassette來源可能和coagulase- negative的Staphylococcus spp.有關, 因此選取了具SCCmec第四型的31株MRSA和36株MRSE, 分別針對基因背景和cassette的結構進行分析彼此間是否具關聯性。 結果發現MRSA和MRSE cassette的結構並不相同, 因此推斷MRSA第四型的cassette由MRSE直接傳遞過來的可能性甚小。 此外第四型的cassette缺少了mecI (repressor), 理論上對於oxacillin的MICs應該極高, 但上述的67株菌種對於oxacillin的MICs分布變異極大, 因此分別從mecA基因序列、promoter region序列、另一個調控的repressor (blaI)的序列和MICs間的關聯性來做探討, 但結果發現彼此間並無關聯性, 因此更進一步的藉Northern Blot的實驗看RNA的表現量和MICs之間的關係, 而結果發現無論MICs的高或低, mecA和blaI的表現量並無明顯差異。又在先前的研究中指出對oxacillin的抗性可能受efflux pump的調控, 因此更近一步的探討當抑制efflux pump的功能時, 對oxacillin的MICs值是否會改變, 而實驗的結果發現MRSE對oxacillin抗性的變異受efflux pump的影響極大, 而MRSA則不受影響, 因此推測造成MRSA抗性的變異可能有其他的因子存在。 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. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/33488 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 醫學檢驗暨生物技術學系 |
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