Exploring the role of C. albicans oxidative stress pathways in S. mutans reactive oxygen species tolerance

Abstract Dental caries is the most prevalent chronic infectious disease, affecting an estimated 2.5 billion people worldwide. Streptococcus mutans is an important pathogen in dental caries due to its ability to acidify the oral pH, inhibiting the growth of health-associated non-aciduric bacteria and narrowing the diversity of the oral microbiota. Candida albicans has emerged as a synergistic partner to S. mutans in dental caries, with the two organisms being co-isolated from early childhood, root, and dentinal caries. Dual-species S. mutans-C. albicans biofilms demonstrate enhanced matrix formation, cariogenicity, and stress tolerance including chlorhexidine and hydrogen peroxide. Hydrogen peroxide has a more than century-long history of oral use for its anti-microbial effect. Many oral hygiene products including mouthwashes and toothpastes incorporate hydrogen peroxide. While hydrogen peroxide has shown to be efficacious as an adjunct in treating periodontitis, its anti-caries effect is less studied. Interestingly, S. mutans is relatively susceptible to oxidative stress in comparison to health-associated oral streptococci. However, the enhanced oxidative stress tolerance of S. mutans in co-culture with C. albicans may reduce hydrogen peroxide's effectiveness as an anti-caries agent. C. albicans encodes a robust set of oxidative stress tolerance genes. Notably, these include 6 superoxide dismutase (SOD) enzymes (3 of which are extracellular) and a catalase enzyme, which detoxify superoxide to hydrogen peroxide and hydrogen peroxide to water, respectively. S. mutans encodes only a single SOD enzyme. Our working hypothesis is that C. albicans oxidative stress tolerance enzymes, catalase and extracellular SODs, enhance S. mutans oxidative stress tolerance in S. mutans-C. albicans biofilms. The goals of this application are to elucidate the mechanism of C. albicans protection of S. mutans oxidative stress tolerance in vitro and in vivo. To accomplish these goals the PI will utilize biofilm, survival, interruption, and confocal microscopy assays (Aim 1) and rat caries model (Aim 2) to determine the roles of C. albicans catalase and extracellular SOD enzymes on S. mutans oxidative stress tolerance and subsequent cariogenicity Knowledge gained from this study will provide a novel target for disruption of S. mutans-C. albicans synergism and the highly cariogenic biofilms these organisms produce. Additionally, the comprehensive training plan provided will further the PI's development to a well-rounded dental researcher through formal coursework, opportunities to learn new techniques, mentor students, improve scientific presenting and writing skills, balancing dental practice and research, and networking with other dentists and scientists at conferences.