Baldassarri Lucilla, Bertuccini Lucia, Ammendolia Maria Grazia, Cocconcelli Pierluigi, Arciola Carla Renata, Montanaro Lucio, Creti Roberta, Orefici Graziella
Laboratorio di Ultrastrutture, Istituto Superiore di Sanità Viale Regina Elina, Rome, Italy.
Indian J Med Res. 2004 May;119 Suppl:131-5.
BACKGROUND & OBJECTIVES: Enterococci are important nosocomial pathogens that are increasingly difficult to treat due to intrinsic and acquired resistance to antibiotics. Studies were taken up to identify virulence factors and to characterise pathogenic mechanisms of such infections to evaluate potential targets for treatments alternative to antibiotic therapy. This study was carried out to evaluate the contribution of extracellular polysaccharide expressed by Enterococcus faecalis to resistance to phagocytosis and survival within rat peritoneal macrophages.
Six E. faecalis clinical isolates were tested for their ability to survive within rat peritoneal macrophages. Cytochalasin D, colchicine and monodansylcadaverine were used to investigate the route of enterococcal entry inside macrophages.
Four of the isolates were able to produce extracellular polysaccharide and form biofilm after growth in glucose-supplemented medium, while no production could be detected in glucose deficient medium. Two isolates were polysaccharide-negative in both conditions. Isolates expressing extracellular polysaccharide were able to survive for more than 24 h compared to polysaccharide-negative bacterial cells of the same strain grown in glucose-deficient medium, which were readily cleared. Cytochalasin D virtually abolished the number of viable intracellular bacteria, after growth in either trypticase soy broth (TSB) or TSB supplemented with glucose; colchicine and monodansylcadaverine strongly affected survival of polysaccharide-positive bacteria, significantly more than that of polysaccharide-negative ones.
INTERPRETATION & CONCLUSION: Biofilm-forming E. faecalis survived within rat peritoneal macrophages significantly better than polysaccharide-negative isolates. Perturbators of cytoskeleton and of surface receptors turnover, indicated receptors-mediated endocytosis as the most likely route for enterococcal entry into macrophages.
肠球菌是重要的医院感染病原菌，由于其对抗生素的固有耐药性和获得性耐药性，治疗难度日益增加。开展相关研究以鉴定毒力因子并表征此类感染的致病机制，从而评估抗生素治疗替代方案的潜在靶点。本研究旨在评估粪肠球菌表达的细胞外多糖对抵抗吞噬作用及在大鼠腹腔巨噬细胞内存活的作用。
检测6株粪肠球菌临床分离株在大鼠腹腔巨噬细胞内存活的能力。使用细胞松弛素D、秋水仙碱和单丹磺酰尸胺研究肠球菌进入巨噬细胞的途径。
4株分离株在补充葡萄糖的培养基中生长后能够产生细胞外多糖并形成生物膜，而在缺乏葡萄糖的培养基中未检测到多糖产生。2株分离株在两种条件下均为多糖阴性。与在缺乏葡萄糖的培养基中生长的同一菌株的多糖阴性细菌细胞相比，表达细胞外多糖的分离株能够存活超过24小时，后者很容易被清除。在胰蛋白胨大豆肉汤（TSB）或补充葡萄糖的TSB中生长后，细胞松弛素D几乎消除了存活的细胞内细菌数量；秋水仙碱和单丹磺酰尸胺强烈影响多糖阳性细菌的存活，对多糖阴性细菌的影响明显更大。
形成生物膜的粪肠球菌在大鼠腹腔巨噬细胞内存活的能力明显优于多糖阴性分离株。细胞骨架和表面受体周转的干扰剂表明，受体介导的内吞作用是肠球菌进入巨噬细胞最可能的途径。
