Enterococcus faecalis affects the proliferation and differentiation of ovine osteoblast-like cells

Enterococcus faecalis (E. faecalis) is a Gram-positive bacterium, mostly recovered from root-filled teeth with persistent periapical lesions. Bacterial contamination of root canals inevitably results in interaction between E. faecalis and periapical tissues during the dynamic process of periapical inflammation. This study investigated the impact of heat-inactivated endodontic E. faecalis on the proliferation and the differentiation of ovine osteoblast-like cells, in an attempt to elucidate its putative enhanced pathogenicity mechanisms. Therefore, two different concentrations of a heat-inactivated endodontic E. faecalis isolate (2 × 106 or 2 × 108 CFU/ml) were incubated with ovine osteoblast-like cells for 7 and 14 days, respectively. Cells without antigen served as control. The effects of antigen on cell growth were evaluated by a proliferation assay (EZ4U). Furthermore, the assessment of alkaline phosphatase (ALP) activity, calcium deposition, and osteocalcin (OCN) gene expression through quantitative real-time PCR determined the degree of osteogenic cell differentiation. Scanning electron microscopy (SEM) was also performed to detect alterations in cell morphology. Interestingly, although highly concentrated E. faecalis increased cellular reproduction after 14 days, ALP activity and OCN gene expression decreased in an antigen concentration-dependent and incubation time-independent way. SEM images revealed E. faecalis adhesion on cells, a fact that might contribute to its virulence. These results suggest that E. faecalis stimulated cell multiplication, whereas it likely restrained cell differentiation of ovine osteoblast-like cells. In conclusion, the presence of E. faecalis in root canals may negatively affect periapical new bone formation, and thus, the healing of periapical lesions.