Enterococcus faecalis persists and replicates within epithelial cells in vitro and in vivo during wound infection

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 an in vitro keratinocyte infection model, we show that a subpopulation of E. faecalis becomes internalized via macropinocytosis into single membrane-bound compartments, where they can survive and replicate. These intracellular E. faecalis can persist in late endosomes up to 72 hours 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 a marked reduction in Rab7 expression, a small GTPase required for endosome-lysosome fusion. 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.