Tendolkar Preeti M, Baghdayan Arto S, Shankar Nathan
Department of Pharmaceutical Sciences, University of Oklahoma Health Sciences Center, P.O. Box 26901, Oklahoma City, OK 73190, USA.
J Bacteriol. 2005 Sep;187(17):6213-22. doi: 10.1128/JB.187.17.6213-6222.2005.
Enterococci have emerged as one of the leading causes of nosocomial bloodstream, surgical site, and urinary tract infections. More recently, enterococci have been associated with biofilms, which are bacterial communities attached to a surface and encased in an extracellular polymeric matrix. The enterococcal cell surface-associated protein, Esp, enhances biofilm formation by Enterococcus faecalis in a glucose-dependent manner. Mature Esp consists of a nonrepeat N-terminal domain and a central region made up of two types of tandem repeats followed by a C-terminal membrane-spanning and anchor domain. This study was undertaken to localize the specific domain(s) of Esp that plays a role in Esp-mediated biofilm enhancement. To achieve this objective, we constructed in-frame deletion mutants expressing truncated forms of Esp in an isogenic background. By comparing strains expressing the mutant forms of Esp to those expressing wild-type Esp, we found that the strain expressing Esp lacking the N-terminal domain formed biofilms that were quantitatively less in biovolume than the strain expressing wild-type Esp. Furthermore, an E. faecalis strain expressing only the N-terminal domain of Esp fused to a heterologous protein anchor formed biofilms that were quantitatively similar to those formed by a strain expressing full-length Esp. This suggested that the minimal region contributing to Esp-mediated biofilm enhancement in E. faecalis was confined to the nonrepeat N-terminal domain. Expression of full-length E. faecalis Esp in heterologous host systems of esp-deficient Lactococcus lactis and Enterococcus faecium did not enhance biofilm formation as was observed for E. faecalis. These results suggest that Esp may require interaction with an additional E. faecalis-specific factor(s) to result in biofilm enhancement.
肠球菌已成为医院血流感染、手术部位感染和尿路感染的主要病因之一。最近，肠球菌与生物膜有关，生物膜是附着在表面并包裹在细胞外聚合物基质中的细菌群落。粪肠球菌细胞表面相关蛋白Esp以葡萄糖依赖的方式增强粪肠球菌的生物膜形成。成熟的Esp由一个非重复的N端结构域和一个中央区域组成，中央区域由两种类型的串联重复序列组成，后面跟着一个C端跨膜和锚定结构域。本研究旨在定位Esp中在Esp介导的生物膜增强中起作用的特定结构域。为了实现这一目标，我们构建了在同基因背景下表达截短形式Esp的框内缺失突变体。通过将表达Esp突变形式的菌株与表达野生型Esp的菌株进行比较，我们发现表达缺失N端结构域的Esp的菌株形成的生物膜在生物体积上比表达野生型Esp的菌株少。此外，仅表达与异源蛋白锚定融合的Esp N端结构域的粪肠球菌菌株形成的生物膜在数量上与表达全长Esp的菌株形成的生物膜相似。这表明在粪肠球菌中，对Esp介导的生物膜增强有贡献的最小区域局限于非重复的N端结构域。在缺乏esp的乳酸乳球菌和屎肠球菌的异源宿主系统中表达全长粪肠球菌Esp并没有像在粪肠球菌中观察到的那样增强生物膜形成。这些结果表明，Esp可能需要与额外的粪肠球菌特异性因子相互作用才能导致生物膜增强。
