表皮葡萄球菌對夫西地酸之抗藥基因及亞型分析

Abstract

夫西地酸 (fusidic acid；FA)為類固醇類的抗生素，臨床上主要用於治療葡萄球菌屬所引起的皮膚感染或者較為嚴重的全身性症狀。細菌在合成蛋白質的過程當中，elongation factor G (EF-G)會與ribosome結合，並協助水解GTP產生能量，將peptidyl-tRNA從A site移至P site，接著EF-G-GDP離開ribosome，繼續蛋白質合成。而夫西地酸會與EF-G-GTP/GDP-ribosome結合，使EF-G-GDP無法離開ribosome而抑制細菌蛋白質的合成，達到藥物作用的效果。 細菌可經由藥物作用標的基因改變 (fusA和fusE 點突變)、獲得外來抗藥基因 (fusB、fusC、fusD)或是其他未知機制而對夫西地酸產生抗藥。fusB最早被發現位於質體pUB101 (transposon-like element)或是染色體核酸 (chromosome DNA；staphylococcal related pathogenicity island)上。有學者證明FusB會與EF-G直接結合，並在夫西地酸存在下使得細菌蛋白質可以順利轉譯達到抗藥的效果。fusC及fusD與fusB相似，同樣會使細菌對於夫西地酸產生抗藥性。 本實驗針對2008年台大醫院145株表皮葡萄球菌臨床菌株，針對其中53株對於夫西地酸抗藥的菌株 (36.6%)，分析抗藥基因的分布情形：其中主要以fusB (52 / 53 =98.1%)為主、fusC (1 / 53 = 1.9%)次之，沒有fusD (0%)。並且利用aj1-LP-fusB結構對fusB進行分型，主要以type II (34.0%)、type III (37.7%)為主，以及少部分的type I (7.5%)，且發現大部分是插入在染色體核酸groEL的下游 (28/52 = 53.8%)；而fusC的結構與MSSA476應該是相似的。為了解分離自不同病患但卻皆帶有fusB基因的表皮葡萄球菌是否為單一菌株傳播或是不同菌株感染，進行脈衝式電泳，其為不同菌株感染，結果顯示帶有fusB的基因片段可能會在臨床菌株中傳播而造成細菌的抗藥性。

Fusidic acid (FA) is a steroid antibiotic that is an effective anti-staphylococcal treatment used for skin or more severe systemic infection by staphylococci. In the process of bacteria protein synthesis, elongation factor G (EF-G) binds to the ribosome, and assists in hydrolysis of GTP to produce energy when the peptidyl-tRNA from the A site to the P site, followed by EF-G-GDP to leave the ribosome, to continue Protein synthesis. Fusidic acid inhibits bacteria protein synthesis by binding to a complex of elongation factor G (EF-G-GTP/GDP-ribosome), and then inhibiting the release of EF-G-GDP complex even after transloacation. Resistance to fusidic acid can arise from the drug target gene alteration (fusA and fusE point mutation), horizontal acquirement of resistance determinants ( fusB, fusC and fusD) or other unknown mechanisms. fusB was first found in the plasmid pUB101 (transposon-like element), or in the chromosomal DNA (staphylococcal related pathogenicity island) ,and then demonstrated directly binding to EF-G to protect staphylococcal translation in vitro. fusC and fusD were homologues of fusB conferred resistance to fusidic acid. In this study, we selected 53 fusidic acid resistant Staphylococcus epidermidis clinical strains (53 / 145 = 36.6%) isolated from the 2008 National Taiwan University Hospital (NTUH). First, we analyzed the distribution of resistance genes: mainly fusB (52 / 53 = 98.1%) , fusC (1 / 53 = 1.9%) and no fusD (0%). And we classified fusB by aj1-LP-fusB structure: type I (7.5%), mainly type II (34.0%) and type III (37.7%). And we found that most strains were inserted in the chromosomal DNA downstream of groEL (28/52 = 53.8%); and fusC structure might be similar with the MSSA476. The pulsed field gel electrophoresis patterns of S. epidermidis NTUH clinical strains showed the heterogeneity and the fusB element maybe transferable among clinical isolates.