Strains of Streptococcus mutans and Streptococcus sobrinus attach to different pellicle receptors

Abstract

We compared the levels of adsorption of Streptococcus mutans JBP and Streptococcus sobrinus 6715 to experimental pellicles formed from unsupplemented and glucosyltransferase (GTF)-supplemented saliva. Pellicles formed on hydroxyapatite beads from GTF or from saliva-GTF mixtures possessed detectable GTF activity. Low levels of GTF activity were also detected in clarified whole human saliva, but not in samples of submandibular saliva. The adsorptive behavior of S. mutans JBP to pellicles formed from saliva or saliva-GTF mixtures was strikingly different from that of S. sobrinus 6715. S. mutans JBP adsorbed in higher numbers to pellicles formed from whole or submandibular saliva than to buffer-treated hydroxyapatite under the assay conditions used, in which blocking with albumin was used. In contrast, S. sobrinus 6715 attached in lower numbers and did not show enhanced adsorption to pellicles prepared from saliva. Pellicles prepared from the high-molecular-weight mucin fraction of submandibular saliva effectively promoted adsorption of S. mutans JBP, but none of the saliva fractions tested enhanced the attachment of S. sobrinus 6715 above the levels of buffer controls. Exposure of pellicles which contained GTF to sucrose to permit in situ synthesis of glucan markedly enhanced attachment of S. sobrinus 6715 but not attachment of S. mutans JBP. Also, the presence of sucrose throughout the adsorption period did not enhance attachment of S. mutans JBP. Both organisms possessed cell-associated GTF, and GTF preparations derived from S. sobrinus 6715 and Streptococcus sanguis FC-1 behaved like GTF derived from S. mutans JBP. S. sobrinus 6715 attached in high numbers to dextran-treated hydroxyapatite, whereas S. mutans JBP did not. These observations suggest that S. mutans JBP cells possess an adhesin which binds to salivary components in the pellicles. In contrast, S. sobrinus 6715 cells appear to possess an adhesin which binds to glucan in the pellicles. Four additional strains of S. mutans and four additional strains of S. sobrinus behaved qualitatively like strains JBP and 6715, respectively, and thus the differences observed appear to be representative of these species. Collectively, our data indicate that S. mutans and S. sobrinus attach to different receptors in experimental pellicles.