Aspirin has antimicrobial activity against endodontic pathogens

Objectives: The use of novel or repurposed drugs is of emerging interest in the drive to combat antimicrobial resistance. In this study we examined the antimicrobial activity of aspirin and its active metabolite salicylic acid against biofilms of endodontic pathogens. Methods: The antimicrobial activities of aspirin and salicylic acid were tested for efficacy against Streptococcus mutans, Lactobacillus acidophilus, Streptococcus sanguinis and Fusobacterium nucleatum in mono-species biofilm disruption assays using a 96 well microtitre plate format. Biofilm biomass was quantified using the crystal violet assay. The potential cytotoxicity of both aspirin and salicylic acid against dental pulp cells was determined by the 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay. All experiments were repeated three times, with four replicates in each experiment. Results: Aspirin was shown to be effective in biofilm disruption assays against all four Gram positive pathogens tested, at concentrations of 0.5mM and above. Biofilms of S. sanguinis and L. acidophilus were shown to be particularly susceptible to aspirin. Biofilms of the Gram negative anaerobe F. nucleatum showed significant reductions in biofilm biomass only following treatment with higher concentrations of aspirin. Salicylic acid was shown to be effective in significantly decreasing biofilm biomass at concentrations above 0.5mM for all five dental pathogens tested. MTT assay results indicated that cytotoxicity against dental pulp cells in vitro was only observed at concentrations of 5mM and above for both salicylic acid and aspirin. Conclusions: The results of this study indicate for the first time that aspirin and its active metabolite salicylic acid have antibiofilm effects against a variety of dental pathogens involved in endodontic infections. Given the drive towards reducing the use of antibiotics, novel antimicrobial activities, such as those presented in the current study, hold much promise for novel therapeutic interventions.