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Title: | 金黃色葡萄球菌及人葡萄球菌中夫西地酸抗藥基因fusC之基因片段分析 Characterization of fusC elements in fusidic acid resistant Staphylococcus aureus and Staphylococcus hominis |
Authors: | Yu-Tzu Lin 林瑜姿 |
Advisor: | 鄧麗珍(Lee-Jene Teng) |
Keyword: | 金黃色葡萄球菌,人葡萄球菌,夫西地酸,fusC,小菌落突變株,fabF, Staphylococcus aureus,Staphylococcus hominis,fusidic acid,fusC,small colony variants,fabF, |
Publication Year : | 2016 |
Degree: | 博士 |
Abstract: | 夫西地酸 (fusidic acid) 為臨床上用於治療葡萄球菌所引起的感染之藥物之一,但細菌可因藥物作用標的基因產生突變或產生保護藥物作用標的的蛋白質 (FusB-protein family) 而產生抗藥性。本實驗收集2008至2010年來臺大醫院細菌室之46株夫西地酸抗藥之抗甲氧西林金黃色葡萄球菌 (methicillin-resistant Staphylococcus aureus, MRSA) 菌株,分析其抗藥基因及分子流行病學。結果顯示,46株夫西地酸抗藥之MRSA菌株中,有19株 (41%) 在fusA基因產生突變,主要以H457Q/L461F及L461K為主,另外有27株 (59%) 帶有fusC基因。帶有fusA基因H457Q/L461F突變之菌株為SCCmec第二型,而帶有其他fusA突變及fusC基因之菌株大多數為SCCmec第三型。另外在PFGE基因分型的結果中顯示,帶有相同抗藥因子的菌株具有較相似的基因型。利用南方墨點法及核酸定序分析MRSA中帶有fusC基因的基因片段結構。結果顯示fusC基因位於一個新SCC基因片段,SCCfusC。SCCfusC,位於rlmH基因的下游及SCCmec片段的上游,並帶有ccrA1B1基因及speG基因。此fusC結構為首次發現,並有可能藉由clonal spread造成對夫西地酸抗藥菌株的增加。
而在凝固酶陰性葡萄球菌中,人葡萄球菌 (S. hominis) 帶有fusC基因的比例較其他菌種來的高。因此,針對人葡萄球菌共蒐集了33株夫西地酸抗藥菌株,其中僅2株帶有fusB基因,而有31株帶有fusC基因。利用PCR偵測其fusC基因的基因片段發現其中14株其fusC基因位於SCCfusC當中,3株位於SCC476。進一步使用核酸定序分析其他位在未知片段之fusC基因上下游序列後得到一個新的SCC基因片段,命名為SCC3390。。除了人葡萄球菌之外,在其他凝固酶陰性葡萄球菌例如表皮葡萄球菌、溶血葡萄球菌及頭狀葡萄球菌中亦偵測到SCCfusC結構,且不同菌種中發現之SCCfusC序列有很高的相似度,推測SCCfusC可於菌種間傳遞。 此外,我們發現有一病人共分離5株菌株,較早收集的3株菌株 (NTUH-9383、NTUH-471及NTUH-1230) 為MRSA,較晚收集的2株菌株 (NTUH-6319及NTUH-7203) 為MSSA (methicillin-susceptible S. aureus),且2株MSSA對daptomycin及teicoplanin有較高的抗性。而在表現型上可發現NTUH-7203具有菌落較小的現象。我們針對NTUH-9383及NTUH-7203進行全基因定序,發現兩株菌株在基因序列上共有13處差異,包含SCCmec基因片段、IS256插入(三處)、8個單點突變(包含 mprF, cls2, clpX and fabF)及1個單一核苷酸的插入。在過去文獻中,mprF及cls2突變被報導與S. aureus產生daptomycin抗藥性有關。NTUH-7203與菌落大小相對正常的NTUH-6319在基因上最明顯的差異為與細菌脂質合成有關的fabF,且外加脂質可讓NTUH-7203的菌落大小恢復,因此fabF突變可能為造成NTUH-7203成為小菌落突變株之主要原因。另外,在電子顯微鏡下發現,除了NTUH-7203之外,NTUH-6319也被觀察到小菌落突變株會有的不正常細胞外觀,推測小菌落突變株的形成是一系列改變所造成。 Fusidic acid is an antibiotic used in treatment against staphylococcal infection. Resistance to fusidic acid in Staphylococcus aureus is caused by alternation of drug target site or by protection of drug target site. In this study, we analyzed the resistance determinants in 46 fusidic acid-resistant methicillin-resistant S. aureus isolates collected from 2008 to 2010, and performed genotyping. The results showed that fusC (59%) was more common than fusA mutations (41%). The most frequent mutation sites in fusA includes L461K (N = 8) and H457Q/L461F (N = 6). Two major genotypes, spa type t037-ST239-SCCmec type III (83%) and t002-ST5- SCCmec type II (11%), were found. A novel SCC structure, termed SCCfusC, was integrated into the rlmH gene and located upstream of SCCmec and was present in all but one (26/27) fusC-carrying MRSA isolates. The SCCfusC also contained speG, which contributed to the polyamine resistance. This is the first report about MRSA isolates that carry both fusC and speG. The fusC carriage in S. hominis was more frequent than other coagulase-negative staphylococci (CoNS). To understand the flanking region of fusC in S. hominis, 31 fusC-positive S. hominis isolates were collected and analyzed the structure of fusC element. The results showed that 14 isolates carried SCCfusC, 3 carried SCC476 and 8 carried new SCC structure, SCC3390. By PFGE and MLST analysis, the S. hominis population showed a limited clonality. Moreover, the SCCfusC was found in other species of CoNS including S. hominis, S. epidermidis, S. haemolyticus and S. capitis, suggesting that SCCfusC may transfer between different species of staphylococci. In this study, there were 5 vancomycin-intermediate S. aureus (VISA) isolates recovered from a same patient. The first three isolates (NTUH-9383, NTUH-471, and NTUH-1230) were MRSA but the latest two (NTUH-6319 and NTUH-7203) were methicillin-susceptible S. aureus (MSSA) and exhibited the characteristics of small colony variants (SCVs). Two MSSA isolates also displayed resistance to daptomycin. Whole genome sequencing of NTUH-9383 and NTUH-7203 indicated that there were 13 differences, including the presence or loss of SCCmec, 8 point mutations (including mprF, cls2, clpX and fabF), a single nucleotide insertion and three IS256 insertions. The most significant difference between NTUH-6319 and NTUH-7203 was the point mutation in fabF encoding fatty acid synthesis enzyme, which may possibly correspond to small colony of NTUH-7203. By high-resolution micrographs, both NTUH-6319 and NTUH-7203 displayed the features of SCV, abnormal intercellular substance. The overall findings suggested that daptomycin treatment may cause the formation of SCV after steps of a serial of changes. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/50705 |
DOI: | 10.6342/NTU201601021 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 醫學檢驗暨生物技術學系 |
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