Due to several factors, including spaceflight osteopenia, decreased saliva production, and immune dysfunction, astronauts are at an increased risk of dental caries. Streptococcus mutans is a commensal pathogen, contributes to tooth decay, and exhibits altered physiology when cultured under simulated microgravity conditions. 

A set of experiments were conducted to investigate the effects of simulated microgravity on oxidative stress tolerance, one of the more well-characterized virulence factors of S. mutans. HARVS (High-Aspect Rotating Vessels) were inoculated with S. mutans UA159 and incubated using two microgravity models (Rotary Cell Culture System vs. Random Positioning Machine), with normal gravity controls. Samples were harvested at endpoints corresponding to mid exponential and late exponential growth phases. Each sample was treated with H2O2. At 30-minute intervals, samples were diluted, plated, and incubated. Time-dependent and dose-dependent effects were observed in the oxidative stress assays. Mid-exponential RCCS cultures were generally more sensitive to oxidative stress compared to late-exponential cultures. Differences were also observed in oxidative stress tolerance between the RPM and RCCS microgravity models, particularly in cultures harvested at late exponential growth.