Contribution of Streptococcus gordonii Hsa Adhesin to Biofilm Formation

Adhesion of oral mitis group streptococci, such as Streptococcus gordonii, to acquired pellicle on the tooth surface is the first step in oral biofilm formation. S. gordonii strain DL1 possesses an Hsa adhesin, which recognizes the terminal sialic acid of host sialoglycoconjugates. The aim of the present study was to investigate the role of the Hsa adhesin in biofilm formation. The biofilm-forming ability of a S. gordonii hsa mutant on microtiter plates pre-coated with saliva, fetuin, or mucin was significantly lower than that of wild-type strain DL1. In contrast, no significant difference in biofilm-forming ability was observed in plates pre-coated with bovine serum albumin, which does not contain sialic acid. The biofilm-forming ability of strain DL1 in saliva-coated microtiter plates was also significantly reduced when the plate was pre-treated with neuraminidase. The sialic acid-dependent biofilm-forming ability of different wild-type S. gordonii strains varied. However, Southern and western blot analyses showed that all the tested wild-type strains possessed and expressed hsa homologs, respectively. These results indicate that the binding of Hsa adhesin to sialoglycoconjugates is associated with biofilm formation of S. gordonii DL1, and imply variation in the contribution of Hsa and its homologs to S. gordonii biofilm formation.