Live and let die: Hydrogen peroxide production by the commensal flora and its role in maintaining a symbiotic microbiome

Summary The majority of commensal oral streptococci are able to generate hydrogen peroxide (H 2 O 2 ) during aerobic growth, which can diffuse through the cell membrane and inhibit competing species in close proximity. Competing H 2 O 2 production is mainly dependent upon the pyruvate oxidase SpxB, and to a lesser extent the lactate oxidase LctO, both of which are important for energy generation in aerobic environments. Several studies point to a broad impact of H 2 O 2 production in the oral environment, including a potential role in biofilm homeostasis, signaling, and interspecies interactions. Here, we summarize the current research regarding oral streptococcal H 2 O 2 generation, resistance mechanisms, and the ecological impact of H 2 O 2 production. We also discuss the potential therapeutic utility of H 2 O 2 for the prevention/treatment of dysbiotic diseases as well as its potential role as a biomarker of oral health.