University Archives

With the increasing use of marijuana, it is vital to understand the effect of tetrahydrocannabinol (THC) on oral microbiota, especially the primary carious pathogen Streptococcus mutans.

The minimum inhibitory concentration (MIC) of THC against S mutans was determined by antimicrobial susceptibility testing. Bacterial acid production was evaluated. The effect of THC on S mutans biofilm formation and preformed biofilms was determined by crystal violet assay. The metabolic activity and viability of the biofilm were assessed using the methylthiazolyldiphenyl tetrazolium bromide assay and live/dead assay, respectively. Extracellular polysaccharide (EPS) was examined by Cascade Blue Dextran staining. S mutans membrane potential was detected by the Baclight Bacterial Membrane Potential Kit.

The MIC of THC against S mutans was 2 µg/mL (P < .0001). A total of ≥2 µg/mL THC reduced bacterial acidogenicity and inhibited over 90% of biofilm formation (P < .0001). Additionally, ≥1 µg/mL THC reduced biofilm viability and EPS production (P < .0001), as assessed by fluorescence measurements and microscopy. While 1 to 64 µg/mL THC did not degrade preformed biofilm, metabolic activity was reduced by 16 to 64 µg/mL THC (P < .01), and 8 to 32 µg/mL THC reduced biofilm viability in a time- and dose-dependent manner (P < .001). Moreover, 2 to 8 µg/mL THC promoted membrane hyperpolarization after a 5-minute treatment (P < .01).

THC inhibits S mutans growth and biofilm formation while also reducing bacterial viability, EPS production, and acid production. Although it does not degrade preformed biofilm biomass, THC diminishes its metabolic activity and viability. These effects may be linked to THC-induced membrane hyperpolarization. This in vitro study suggests that THC may reduce the cariogenic capacity of S mutans.