Supplementary Material for: Diversity in Antagonistic Interactions between Commensal Oral Streptococci and Streptococcus mutans

<p>Arginine metabolism via the arginine deiminase system (ADS) of oral bacteria generates ammonia, which can increase the pH of oral biofilms and decrease the risk for dental caries. Antagonistic interactions between ADS-positive and cariogenic bacteria in oral biofilms may be an important ecological determinant of caries. This study investigated the antagonistic potential and mechanisms of clinical isolates of arginolytic streptococci on and by <i>Streptococcus mutans </i>UA159, a well-characterized cariogenic human isolate. Low-passage isolates of <i>Streptococcus gordonii</i>, <i>Streptococcus sanguinis</i>, <i>Streptococcus parasanguinis, Streptococcus australis</i>, and <i>Streptococcus cristatus</i> inhibited the growth of <i>S. mutans </i>to various degrees when they were inoculated on growth media first or simultaneously with <i>S. mutans</i>. The antagonistic effects of arginolytic strains against <i>S. mutans </i>and the production of H<sub>2</sub>O<sub>2</sub> by these strains were enhanced during growth in a less-rich medium or when galactose was substituted for glucose as the primary carbohydrate source. Pyruvate oxidase was the dominant pathway for H<sub>2</sub>O<sub>2</sub> production by arginolytic strains, but lactate oxidase activity was also detected in some strains of <i>S. gordonii</i> and<i> S. cristatus. </i>UA159 inhibited the growth of all tested arginolytic strains when inoculated first, especially in aerobic conditions. However, the antagonistic effects of <i>S. mutans </i>on certain strains of <i>S. gordonii</i> and<i> S. australis</i> were not observed during anaerobic growth in the presence of arginine. Thus, arginolytic commensal streptococci may have a synergistically positive impact on the ecology of oral biofilms by moderating biofilm pH while antagonizing the growth and virulence of caries pathogens.</p>