Antibacterial effects of N-acetylcysteine against endodontic pathogens.

The success of endodontic treatment depends on the eradication of microorganisms from the root canal system and the prevention of reinfection. The purpose of this investigation was to evaluate the antibacterial and antibiofilm efficacy of N-acetylcysteine (NAC), an antioxidant mucolytic agent, as an intracanal medicament against selected endodontic pathogens. Minimum inhibitory concentrations (MICs) of NAC for Actinomyces naeslundii, Lactobacillus salivarius, Streptococcus mutans, and Enterococcus faecalis were determined using the broth microdilution method. NAC showed antibacterial activity, with MIC values of 0.78-1.56 mg/ml. The effect of NAC on biofilm formation of each bacterium and a multispecies culture consisting of the four bacterial species was assessed by crystal violet staining. NAC significantly inhibited biofilm formation by all the monospecies and multispecies bacteria at minimum concentrations of 0.78-3.13 mg/ml. The efficacy of NAC for biofilm disruption was evaluated by scanning electron microscopy and ATP-bioluminescence quantification using mature multispecies biofilms. Preformed mature multispecies biofilms on saliva-coated hydroxyapatite disks were disrupted within 10 min by treatment with NAC at concentrations of 25 mg/ml or higher. After 24 h of treatment, the viability of mature biofilms was reduced by > 99% compared with the control. Moreover, the biofilm disrupting activity of NAC was significantly higher than that of saturated calcium hydroxide or 2% chlorhexidine solution. Within the limitations of this in vitro study, we conclude that NAC has excellent antibacterial and antibiofilm efficacy against endodontic pathogens and may be used as an alternative intracanal medicament in root canal therapies.