Department of Medical Microbiology, University Medical Center Utrecht, Heidelberglaan 100; Room G04,527, Utrecht, 3584 CX, The Netherlands.
BMC Genomics. 2013 May 3;14:299. doi: 10.1186/1471-2164-14-299.
Enterococcus faecium is a Gram-positive commensal bacterium of the mammalian intestinal tract. In the last two decades it has also emerged as a multi-resistant nosocomial pathogen. In order to survive in and colonize the human intestinal tract E. faecium must resist the deleterious actions of bile. The molecular mechanisms exploited by this bacterium to tolerate bile are as yet unexplored.
In this study we used a high-throughput quantitative screening approach of transposon mutant library, termed Microarray-based Transposon Mapping (M-TraM), to identify the genetic determinants required for resistance to bile salts in E. faecium E1162. The gene gltK, which is predicted to encode a glutamate/aspartate transport system permease protein, was identified by M-TraM to be involved in bile resistance. The role of GltK in bile salt resistance was confirmed by the subsequent observation that the deletion of gltK significantly sensitized E. faecium E1162 to bile salts. To further characterize the response of E. faecium E1162 to bile salts, we performed a transcriptome analysis to identify genes that are regulated by exposure to 0.02% bile salts. Exposure to bile salts resulted in major transcriptional rearrangements, predominantly in genes involved in carbohydrate, nucleotide and coenzyme transport and metabolism.
These findings add to a better understanding of the molecular mechanisms by which E. faecium responds and resists the antimicrobial action of bile salts.
屎肠球菌是哺乳动物肠道中的革兰氏阳性共生菌。在过去的二十年中，它也已成为一种多耐药的医院获得性病原体。为了在人类肠道中生存和定植，屎肠球菌必须抵抗胆汁的有害作用。该细菌耐受胆汁的分子机制尚未得到探索。
在这项研究中，我们使用了一种称为基于微阵列的转座子图谱（M-TraM）的高通量定量筛选转座子突变文库的方法，以鉴定屎肠球菌 E1162 中抵抗胆汁盐所需的遗传决定因素。gltK 基因，预测编码谷氨酸/天冬氨酸运输系统通透酶蛋白，通过 M-TraM 被鉴定为参与胆汁抵抗。gltK 在胆汁盐抵抗中的作用通过随后观察到 gltK 的缺失使屎肠球菌 E1162 对胆汁盐的敏感性显著增加而得到证实。为了进一步表征屎肠球菌 E1162 对胆汁盐的反应，我们进行了转录组分析，以鉴定受 0.02%胆汁盐暴露调节的基因。暴露于胆汁盐导致主要的转录重排，主要涉及碳水化合物、核苷酸和辅酶的运输和代谢。
这些发现有助于更好地理解屎肠球菌响应和抵抗胆汁盐抗菌作用的分子机制。
