The Resistance of Collagen-associated, Planktonic Cells of Enterococcus faecalis to Calcium Hydroxide

This study examined whether collagen association by an endodontic isolate of Enterococcus faecalis conferred resistance to the bacterium against calcium hydroxide. E. faecalis A197A was grown at 46°C until early stationary phase. Standardized bacterial suspensions were pretreated for 1 hour either with acid-soluble collagen or acidified phosphate-buffered saline (ac-PBS) and cultured to determine the baseline viable bacterial numbers. The bacterial suspensions were challenged with calcium hydroxide solution. Samples were removed at 6, 12, and 24 hours and cultured on tryptone soy agar plates. An adherence assay was performed to confirm that the collagen in the pretreatment medium was bound by the bacteria. Significantly more bacteria were cultivated at 12 hours in the collagen-pretreated group than the ac-PBS–pretreated group (p < 0.01). No bacteria could be cultivated at 24 hours in either group. Collagen association by E. faecalis A197A was found to increase the tolerance of the bacterium to calcium hydroxide.