In mixed biofilms Enterococcus faecalis benefits from a calcium hydroxide challenge and culturing.

Abstract

To evaluate the fate of Enterococcus faecalis in dual-species and multispecies biofilms after treatment with calcium hydroxide (Ca(OH)2 ). Biofilms were cultured from laboratory strains of E.faecalis and Pseudomonas aeruginosa, or from microbiota retrieved from primary root canal infections. The biofilms were then treated with Ca(OH)2 . The proportion of E.faecalis and P.aeruginosa and their susceptibility to disinfection were evaluated in a viability assay. In the mixed-species assay, the presence and proportions of E.faecalis before and after Ca(OH)2 treatment were evaluated with a quantitative polymerase chain reaction assay. Groups were compared using Mann-Whitney U-test and Student's t-tests. An α <0.05 was considered statistically significant. After Ca(OH)2 treatment in dual-species biofilms, the proportion of E.faecalis had increased (P<0.001), whereas the total number of CFUs per biofilm was equal. Enterococcus faecalis was equally susceptible to disinfection by sodium hypochlorite (NaOCl) or by chlorhexidine. Pseudomonas aeruginosa had become more susceptible to NaOCl disinfection. The root canal isolates contained no detectable amounts of E.faecalis. After biofilm culturing or Ca(OH)2 treatment, it appeared that E.faecalis must have been present in 5 of 6 (83%) root canal samples. Calcium hydroxide favours the population of E.faecalis in a dual-species biofilm. Culturing multispecies root canal isolates makes E.faecalis detectable.E.faecalis was often present in primary endodontic infections, albeit in low numbers.