Surface protein Esp enhances pro-inflammatory cytokine expression through NF-κB activation during enterococcal infection.

Enterococcal surface protein (Esp) is encoded on a pathogenicity island in Enterococcus faecalis and E. faecium and is involved in biofilm formation and binding to epithelial cells. In this study， using Esp-expressing E. faecalis MMH594 and its isogenic Esp-deficient strain， as well as purified Esp， we show that Esp is sufficient for activation of NF-κB and the subsequent production of pro-inflammatory cytokines IL-1β and TNF-α in macrophages in vitro. In a mouse peritonitis model， we also show that mice infected with Esp-expressing E. faecalis showed comparatively higher levels of cytokines TNF-α， IL-1β and IL-6 in peritoneal fluid， and IL-6 in serum. Moreover， neutrophil infiltration and tissue damage in the liver was higher in the mice infected with the Esp-expressing strain compared with mice infected with the Esp-deficient mutant. These results add Esp to the growing list of enterococcal virulence factors that can modulate inflammation during infection and has implications for enterococcal pathogenesis.