PROJECT SUMMARY Vaping of aerosolized tobacco and cannabis products using electronic nicotine delivery devices (ENDS) is increasingly popular among adolescents and young adults. The associated emerging health crisis has significant systemic and oral health implications as nicotine (N) consumption is highly correlated with caries, the most prevalent oral disease in adolescents (57%) and young adults (82%), with cannabis use seemingly having a similar effect. Studies have shown that pure N enhances the growth and biofilm formation of the major cariogenic species Streptococcus mutans (Sm) and Candida albicans (Ca), which entertain a synergistic interkingdom relationship that is considered an important etiological factor in caries development. Limited recent studies on tetrahydrocannabinol (THC), the cannabis product favored by younger age groups, indicated that THC- containing cannabis smoke condensates stimulate the growth and biofilm formation of Ca. Despite emerging evidence supporting the pathogenicity-enhancing consequences of tobacco and cannabis product use, most research has used pure N instead of the more relevant vape aerosol (VA) containing N (N- VA) produced by ENDS. In addition, studies examining the effects of THC or VA containing THC (THC-VA) on Sm and Ca are very limited. Our published research and preliminary data show that the responses of Ca and Sm to pure N are distinct from responses to N-VA at the same N content (as determined by high-performance liquid chromatography). Therefore, we hypothesize that the enhancing effects of VAs containing N and THC result in different synergistic Sm–Ca cariogenic activities than the same concentrations of pure N and THC. In Aim 1, we will investigate the impact of N-VA and THC-VA on the Sm–Ca relationship compared with pure N, pure THC, and control VA (lacking N or THC) using well-characterized lab strains to evaluate co-adhesion, biofilm formation, extracellular polymeric substance production, acid production, and transcriptional responses. In Aim 2, we will validate selected findings from Aim 1 in clinically relevant Sm and Ca strains isolated from adolescent and young adult N and THC vapers as well as non-users with dental caries. We will characterize biofilm formation, acid production, and the highly differentially expressed genes identified in Aim 1. We expect to find that N-VA and THC-VA have distinct effects on the Sm–Ca relationship compared to their respective pure compounds or control VA. Evaluation of transcriptional responses in conjunction with cariogenic behaviors may provide physiological explanations for some of these differences. The results obtained from clinical strains isolated from different vaping environments will (1) validate findings obtained with Sm and Ca lab strains and (2) elucidate whether strains isolated from individuals who vape exhibit distinct responses to N-VA and THC-VA compared to strains isolated from non-users. The knowledge generated by this study w...