Clonal diversity in biofilm formation by Enterococcus faecalis in response to environmental stress associated with endodontic irrigants and medicaments

Abstract

Aim: To determine whether clonal diversity within E. faecalis affects biofilm formation when exposed to antimicrobial compounds found in endodontic medicaments and irrigants.

Methodology: Five human isolates of E. faecalis were compared; biofilms were grown in microtitre trays in the presence of sodium hypochlorite, calcium hydroxide, chlorhexidine, tetracycline or clindamycin. Biofilms were quantified by staining with crystal violet and optical density determined with a microplate reader. Slime production (an amorphous extracellular matrix comprising polysaccharides, glycoproteins and glycolipids loosely attached to the cell surface) was determined qualitatively by growth on Congo red agar plates. Linear mixed models were used to examine whether medicaments affected biofilm growth of the isolates in the presence of the medicaments or irrigants.

Results: Overall, different endodontic antimicrobials significantly altered biofilm growth in E. faecalis isolates. Two E. faecalis isolates significantly (P < 0.0001) increased biofilm formation in the presence of tetracycline and one in the presence of NaOCl (P = 0.018). Qualitatively, slime production also varied between isolates and correlated with biofilm production.

Conclusions: When subjected to sub-minimum inhibitory concentration (MIC) levels of antimicrobial compounds found in endodontic medicaments, E. faecalis isolates demonstrated significant clonal variation in their capacity to form biofilms. Interestingly, there was a correlation between slime production and the ability of isolates to form a biofilm in the presence of antimicrobials. The results indicate that isolates of E. faecalis that form biofilms in response to endodontic medicaments may be more likely to survive endodontic treatment.

Keywords: Enterococcus faecalis; biofilm; endodontics; stress response.