Antigen I/II mediates interactions between Streptococcus mutans and Candida albicans

SUMMARY Streptococcus mutans and Candida albicans are frequently co-isolated from dental plaque of children with early childhood caries (ECC), and only rarely found in non-ECC children, suggesting that these species interact in a manner that contribute to the pathogenesis of ECC. Previous studies have demonstrated that glucans produced by S. mutans are crucial for promoting biofilm formation and cariogenicity with C. albicans; however, it is unclear how non-glucan S. mutans biofilm factors contribute to increased biofilm formation in the presence of C. albicans. In this study, we examined the role of S. mutans antigen I/II in two-species biofilms with C. albicans, and determined that antigen I/II is important for the incorporation of C. albicans into the two-species biofilm, and is also required for increased acid production. The interaction is independent of Als1 and Als3 proteins, which are known streptococcal receptors of C. albicans. Moreover, antigen I/II is required for the colonization of both S. mutans and C. albicans during co-infection of Drosophila melanogaster in vivo. Taken together, these results demonstrate that antigen I/II mediates the increase of C. albicans numbers and acid production in the two-species biofilm, which represents new activities associated with this known S. mutans adhesin.