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

Streptococcus mutans and Candida albicans are frequently co-isolated from dental plaque of children with early childhood caries (ECC) and are only rarely found in children without ECC, suggesting that these species interact in a manner that contributes to the pathogenesis of ECC. Previous studies have demonstrated that glucans produced by S.mutans are crucial for promoting the formation of biofilm 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 the proteins Als1 and Als3, 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, representing new activities associated with this known S.mutans adhesin.