表皮葡萄球菌夫西地酸抗藥基因分型

Abstract

夫西地酸 (fusidic acid)為類固醇類抗生素，藉由與EF-G-GTP/GDP-ribosome結合，使EF-G/GDP無法離開ribosome，抑制細菌蛋白質的合成，臨床上主要用於治療葡萄球菌引起的皮膚感染和較為嚴重的全身性症狀。細菌可經由藥物作用的標的基因產生突變 (fusA或rplF點突變)或表現保護藥物作用標的之蛋白質 (FusB-protein family)來產生抗藥性。之前研究發現表皮葡萄球菌的fusB位在phage-related resistance island中，被認為可能在葡萄球菌屬或是其他菌種間夫西地酸抗藥性傳播扮演重要角色，Chen 等人於2011年發表之報告中表皮葡萄球菌為隨機選自臺大醫院2003~2007年菌株，菌株數較為不足，因此本實驗室針對2008年菌株做一較完整分析。為長期追蹤菌株有無差異，繼續分析臺大醫院2009年所有表皮葡萄球菌夫西地酸抗藥菌株。 本實驗針對2009年臺大醫院136株表皮葡萄球菌臨床菌株分析，40株為夫西地酸抗藥 (29.4％)，大部分帶有fusB (39/40，97.5％)，其中1株為fusA點突變 (P404L)。fusB大部分位於groEL下游 (33/39，84.6％)，少數位在rpsR下游 (1/39，2.6％)，剩餘5株菌株的insertion site仍未知。進一步分析fusB亞型，主要為第二型 aj1-LP-fusB (18/39，46.1％)和第三型 aj1-LP-fusB (15/39，38.5％)，及2株第一型 aj1-LP-fusB (2/39，5.1％)、4株為未知型 (10.3％)。帶有第二型aj1-LP-fusB片段菌株的最小抑菌濃度 (MIC) 相較於帶有第三型aj1-LP-fusB菌株有較高的趨勢。 分析aj1-LP-fusB未知型NTUH857 fusB旁基因序列，Composite SeRIfusB-857基因結構包含SeRIfusB-857 (S. epidermidis resistance island carrying fusB in NTUH857)及SeCI857 (S. epidermidis chromosomal insertion in NTUH857)，SeRIfusB-857上帶有毒力因子VirE和抗藥基因fusB，SeCI857是跳動基因ISSep1-like transposase帶至SeRIfusB-857後的基因序列，含有terminase small subunit和數個hypothetical proteins。 Composite SeRIfusB-857位於SsrA-binding protein下游，Na+-transporting ATP synthase的上游，attc site為TCCCGCCGTCTCCAT，全長21609 bp，由28個ORFs和△aj3組成，G+C content為30.48％。 利用脈衝式電泳分析夫西地酸抗藥菌株的pulsotypes，在＞80％相似性的情形下，40株菌株可以分成18群集 (clusters)，顯示表皮葡萄球菌造成的感染，並非單一菌株的傳播。

Fusidic acid (FA) is a steroid antibiotic that inhibits bacteria protein synthesis by binding to a complex of elongation factor G (EF-G-GTP/GDP-ribosome), and thus inhibits the release of EF-G-GDP complex after translocation. Fusidic acid is an effective antibiotic for skin or severer systemic infection by staphylococci in clinical use. The understanding of fusidic acid resistance mechanisms can be related to alterations in EF-G structure (fusA or rplF point mutation) or to acquisition of the fusidic acid resistance genes (fusB, fusC, fusD). Previous studies demonstrated that fusB genes in Staphylococcus epidermidis were highly associated with phage-related resistance islands (RIs), may be responsible for the dissemination of fusidic acid resistance in S. epidermidis through horizontal gene transfer. In this study, we collected 40 clinical strains of fusidic acid resistant S. epidermidis from National Taiwan University Hospital in 2009. The distribution of resistance genes is mainly fusB (39/40, 97.5％) and one of them is fusA point mutation P404L (1/40, 2.5％). Further identification of the genetic structures of fusB resistance islands among 39 isolates, the results indicated that 33 isolates were flanked by groEL (33/39, 84.6％), 1 was flanked by rpsR (1/39, 2.6％) and 5 isolates remained unknown. Subtyping of aj1-LP-fusB fragments for 39 isolates, revealed that 2 were type I, 18 type II, 15 type III and 4 were undetermined type. Isolates carrying type II aj1-LP-fusB fragments showed relatively higher levels of fusidic acid resistance. The aj1-LP-fusB undetermined strain NTUH857 is located on phage-related resistance island (RI). Composite SeRIfusB-857 was composed of 28 ORFs and △aj3. The gene organization of composite SeRIfusB-857 can be divided into two distinct regions. SeRIfusB-857 (S. epidermidis resistance island carrying fusB in NTUH857) contained virulence factor VirE and resistance gene fusB, and SeCI857 (S. epidermidis chromosomal insertion in NTUH857) contained transposase and several hypothetical proteins. Composite SeRIfusB-857 island is downstream of SsrA-binding protein and upstream of Na+-transporting ATP synthase, attc site was TCCCGCCGTCTCCAT, size of composite SeRIfusB-857 was 21609 bp and G+C content was 30.48％. The pulsotypes of fusidic acid resistant S. epidermidis were heterogenous and not single clone expansion.