Investigation of infection and survival mechanisms held by Enterococcus faecalis (strain A197A): with respect to endodontic disease

Investigation of infection and survival mechanisms held by Enterococcus faecalis (strainA197A): with respect to endodontic diseaseGüven KayaoğluThe aim of this thesis was to explain how Enterococcus faecalis becomes adherent to collagen(the major organic component of the dentine) and survives endodontic disinfection withcalcium hydroxide (Ca(OH)2). Three hypotheses were tested: 1) growth under stress increasesbacterial adhesion to collagen, 2) adhesion to collagen protects the bacterium againstCa(OH)2, 3) growth under stress increases bacterial resistance against Ca(OH)2. E.faecalisA197A, a persistent endodontic infection isolate, was used for the experiments. 1) Bacteriawere grown at 37ºC in broth of adjusted pHs varying between 7.1 and 9.5, and also in brothof 7.1, but at 46ºC (an established stressful growth condition). Bacterial suspensions wereadded to collagen-coated wells. Bacteria adhering to the surfaces were stained with crystalviolet and quantified spectrophotometrically. Adherence to collagen was significantly more inpH 8.0 and 8.5 groups (the latter was also found to be a stressful condition) and in 46ºC-grown group than the other groups (p<0.05). 2) Bacteria were grown at 46ºC and pre-treatedwith collagen or PBS. The bacteria were then challenged with Ca(OH)2. Samples were drawnthroughout 24h and cultured. Bacteria adhering to collagen survived the Ca(OH)2 challengebetter than the control groups at 12h (p<0.01). 3) Bacteria were grown at 37ºC or 46ºC, andchallenged with Ca(OH)2. Samples were drawn throughout 24h and cultured. Bacteria grownat 46ºC survived the Ca(OH)2 challenge better than bacteria grown at 37ºC, at 6h, 12h and18h (p<0.01). The hypotheses were thus confirmed. These may be critical mechanisms bywhich E.faecalis predominates in persistent endodontic infections.