Dale Jennifer L, Cagnazzo Julian, Phan Chi Q, Barnes Aaron M T, Dunny Gary M
Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
Antimicrob Agents Chemother. 2015 Jul;59(7):4094-105. doi: 10.1128/AAC.00344-15. Epub 2015 Apr 27.
The emergence of multidrug-resistant bacteria and the limited availability of new antibiotics are of increasing clinical concern. A compounding factor is the ability of microorganisms to form biofilms (communities of cells encased in a protective extracellular matrix) that are intrinsically resistant to antibiotics. Enterococcus faecalis is an opportunistic pathogen that readily forms biofilms and also has the propensity to acquire resistance determinants via horizontal gene transfer. There is intense interest in the genetic basis for intrinsic and acquired antibiotic resistance in E. faecalis, since clinical isolates exhibiting resistance to multiple antibiotics are not uncommon. We performed a genetic screen using a library of transposon (Tn) mutants to identify E. faecalis biofilm-associated antibiotic resistance determinants. Five Tn mutants formed wild-type biofilms in the absence of antibiotics but produced decreased biofilm biomass in the presence of antibiotic concentrations that were subinhibitory to the parent strain. Genetic determinants responsible for biofilm-associated antibiotic resistance include components of the quorum-sensing system (fsrA, fsrC, and gelE) and two glycosyltransferase (GTF) genes (epaI and epaOX). We also found that the GTFs play additional roles in E. faecalis resistance to detergent and bile salts, maintenance of cell envelope integrity, determination of cell shape, polysaccharide composition, and conjugative transfer of the pheromone-inducible plasmid pCF10. The epaOX gene is located in a variable extended region of the enterococcal polysaccharide antigen (epa) locus. These data illustrate the importance of GTFs in E. faecalis adaptation to diverse growth conditions and suggest new targets for antimicrobial design.
多重耐药菌的出现以及新型抗生素的有限供应日益引起临床关注。一个复杂因素是微生物形成生物膜（包裹在保护性细胞外基质中的细胞群落）的能力，而生物膜本身对抗生素具有抗性。粪肠球菌是一种机会致病菌，很容易形成生物膜，并且有通过水平基因转移获得耐药决定因素的倾向。由于临床分离株对多种抗生素表现出耐药性并不罕见，因此人们对粪肠球菌固有和获得性抗生素耐药性的遗传基础有着浓厚兴趣。我们使用转座子（Tn）突变体文库进行了遗传筛选，以鉴定粪肠球菌生物膜相关的抗生素耐药决定因素。五个Tn突变体在无抗生素的情况下形成野生型生物膜，但在低于亲本菌株抑菌浓度的抗生素存在下，生物膜生物量减少。负责生物膜相关抗生素耐药性的遗传决定因素包括群体感应系统的组成部分（fsrA、fsrC和gelE）以及两个糖基转移酶（GTF）基因（epaI和epaOX）。我们还发现，GTF在粪肠球菌对去污剂和胆盐的抗性、维持细胞膜完整性、确定细胞形状、多糖组成以及信息素诱导质粒pCF10的接合转移中发挥额外作用。epaOX基因位于肠球菌多糖抗原（epa）位点的可变延伸区域。这些数据说明了GTF在粪肠球菌适应不同生长条件中的重要性，并为抗菌设计提出了新的靶点。
