Novel macrolide-resistance genes, mef(C) and mph(G), carried by plasmids from Vibrio and Photobacterium isolated from sediment and seawater of a coastal aquaculture site
Novel macrolide-resistance genes, mef(C) and mph(G), carried by plasmids from Vibrio and Photobacterium isolated from sediment and seawater of a coastal aquaculture site
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DOI：
10.1111/lam.12414
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发表时间：
2015-07-01
影响因子：
2.4
通讯作者：
Masuda, M.
中科院分区：
文献类型：
--
作者：
Nonaka, L.;Maruyama, F.;Masuda, M.
本研究的目的是确定最初在来自发光杆菌胭脂鱼亚种的可转移的多药物质粒pAQU 1上发现的mef（C）和mph（G）是否与来自发光杆菌胭脂鱼亚种的可转移的多药物质粒pAQU 1上发现的mef（C）和mph（G）相同。从养鱼场的海水中分离的豆娘（damselae）负责赋予大环内酯类抗性。由于这些基因在pAQU 1上是首尾相连的，并且它们之间仅存在四个核苷酸，因此检查了这些基因的单一和组合效应。当mph（G）单独引入大肠杆菌时，对红霉素、克拉霉素和阿奇霉素的最小抑菌浓度（MIC）增加，而单独引入mef（C）不影响大环内酯类药物的敏感性。同时引入mef（C）和mph（G）显著增加了对相同三种大环内酯的MIC，即分别> 512 gml（-1）、> 512 gml（-1）和128 gml（-1）。这些结果表明，由mph（G）编码的大环内酯磷酸转移酶是大环内酯耐药所必需的，而由mef（C）编码的外排泵是高水平大环内酯耐药所必需的。从养鱼场获得的22株弧菌属和发光杆菌属红霉素抗性菌株的mef（C）和mph（G）基因在240 ~ 350 kb的质粒上是保守的。22个质粒中有16个大小在300 ~ 350 kb之间。本研究首次发现了海洋细菌来源的新的大环内酯类耐药基因，其中mef（C）和mph（G）是新的大环内酯类耐药基因，这是首次报道海洋细菌来源的大环内酯类耐药基因。这些基因可能是以前报告的情况下，出现的红霉素耐药细菌在水产养殖场的一个未知的机制负责。在大肠杆菌中引入串联排列的mef（C）和mph（G）基因增加了红霉素、克拉霉素和阿奇霉素的MIC，表明通过外排泵和大环内酯磷酸转移酶的联合表达赋予高水平大环内酯耐药性的新机制。
The aim of this study was to determine whether mef(C) and mph(G), originally found on the transferable multi-drug plasmid pAQU1 from Photobacterium damselae subsp. damselae isolated from seawater of a fish farm, are responsible for conferring macrolide resistance. Since these genes are localized head-to-tail on pAQU1 and only four nucleotides exist between them, the single- and combination-effect of these genes was examined. When mph(G) alone was introduced to Escherichia coli, the minimum inhibitory concentrations (MICs) against erythromycin, clarithromycin and azithromycin increased, whereas introduction of mef(C) alone did not influence macrolide susceptibility. Introduction of both mef(C) and mph(G) dramatically increased the MICs to the same three macrolides, i.e. >512gml(-1), >512gml(-1) and 128gml(-1) respectively. These results suggest that the macrolide phosphotransferase encoded by mph(G) is essential for macrolide resistance, while the efflux pump encoded by mef(C) is required for high-level macrolide resistance. The tandem-pair arrangements of the mef(C) and mph(G) genes were conserved on plasmids ranging in size from 240 to 350kb of the 22 erythromycin-resistant strains belonging to Vibrio and Photobacterium obtained from the fish farm. Sixteen of 22 plasmids ranged in size from 300 to 350kb. This is the first report of novel macrolide resistance genes originating from a marine bacterium.Significance and Impact of the StudyIn this study, mef(C) and mph(G) were found to be novel macrolide-resistance genes, and this is the first report of macrolide-resistance genes originating from a marine bacterium. These genes may be responsible for previously reported cases of the emergence of erythromycin-resistant bacteria in aquaculture sites by an unknown mechanism. The introduction of the tandem arrangement of the mef(C) and mph(G) genes in Escherichia coli increased the MICs to erythromycin, clarithromycin and azithromycin, suggesting a novel mechanism conferring high-level macrolide resistance via combined expression of the efflux pump and macrolide phosphotransferase.