Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore.
Singapore-MIT Alliance for Research and Technology, Antimicrobial Drug Resistance Interdisciplinary Research Group, Singapore.
PLoS Pathog. 2022 Apr 7;18(4):e1010434. doi: 10.1371/journal.ppat.1010434. eCollection 2022 Apr.
Enterococcus faecalis is a frequent opportunistic pathogen of wounds, whose infections are associated with biofilm formation, persistence, and recalcitrance toward treatment. We have previously shown that E. faecalis wound infection persists for at least 7 days. Here we report that viable E. faecalis are present within both immune and non-immune cells at the wound site up to 5 days after infection, raising the prospect that intracellular persistence contributes to chronic E. faecalis infection. Using in vitro keratinocyte and macrophage infection models, we show that E. faecalis becomes internalized and a subpopulation of bacteria can survive and replicate intracellularly. E. faecalis are internalized into keratinocytes primarily via macropinocytosis into single membrane-bound compartments and can persist in late endosomes up to 24 h after infection in the absence of colocalization with the lysosomal protease Cathepsin D or apparent fusion with the lysosome, suggesting that E. faecalis blocks endosomal maturation. Indeed, intracellular E. faecalis infection results in heterotypic intracellular trafficking with partial or absent labelling of E. faecalis-containing compartments with Rab5 and Rab7, small GTPases required for the endosome-lysosome trafficking. In addition, E. faecalis infection results in marked reduction of Rab5 and Rab7 protein levels which may also contribute to attenuated Rab incorporation into E. faecalis-containing compartments. Finally, we demonstrate that intracellular E. faecalis derived from infected keratinocytes are significantly more efficient in reinfecting new keratinocytes. Together, these data suggest that intracellular proliferation of E. faecalis may contribute to its persistence in the face of a robust immune response, providing a primed reservoir of bacteria for subsequent reinfection.
粪肠球菌是一种常见的机会性病原体,可引起伤口感染,其感染与生物膜形成、持续存在以及对治疗的耐药性有关。我们之前已经表明,粪肠球菌伤口感染至少持续 7 天。在这里,我们报告说,在感染后 5 天内,免疫和非免疫细胞内仍存在有活力的粪肠球菌,这表明细胞内持续存在可能导致慢性粪肠球菌感染。我们使用体外角质形成细胞和巨噬细胞感染模型,表明粪肠球菌可以被内化,并且一部分细菌可以在细胞内存活和复制。粪肠球菌主要通过巨胞饮作用进入单层膜结合的隔室而被内化到角质形成细胞中,并在感染后 24 小时内可以在没有与溶酶体蛋白酶组织蛋白酶 D 共定位或明显与溶酶体融合的情况下在晚期内体中持续存在,这表明粪肠球菌阻止了内体成熟。事实上,细胞内粪肠球菌感染会导致异型细胞内运输,部分或完全缺乏 Rab5 和 Rab7 的标记,Rab5 和 Rab7 是内体-溶酶体运输所需的小 GTPase。此外,粪肠球菌感染导致 Rab5 和 Rab7 蛋白水平的显著降低,这也可能导致将 Rab 纳入包含粪肠球菌的隔室的能力减弱。最后,我们证明了来自感染角质形成细胞的细胞内粪肠球菌在重新感染新的角质形成细胞方面效率更高。总之,这些数据表明,粪肠球菌的细胞内增殖可能有助于其在强大的免疫反应中持续存在,为随后的再次感染提供了细菌的预存库。