Role of a cell surface-associated protein in adherence and dental caries.

Insertional inactivation of the Streptococcus mutans spaP gene was used to construct an isogenic mutant (834) of strain NG8 (serotype c) which lacked the major cell surface-associated protein referred to as P1 (15). Results of several studies suggest that P1 is involved in the adherence of S. mutans to saliva-coated apatite surfaces. With an in vitro model system of hydroxyapatite (HA) beads coated with parotid saliva (PS) and additional HA surfaces coated with PS and in situ-formed glucan, it was observed that mutant 834 adhered poorly to the PS/HA surfaces. In contrast, both parent and mutant strains bound to the PS-glucan/HA surface. Groups of intact and desalivated rats were infected with each strain to determine relative capacities to induce dental caries. Rats were fed a highly cariogenic diet containing 56% sucrose for 3 to 5 weeks. Each strain colonized the rodent model and caused similar levels of smooth-surface caries under these dietary conditions. It was concluded that P1 influences the ability of organisms to adhere to saliva-coated surfaces and possibly affects primary colonization of the oral cavity in the absence of a glucan surface but has no effect on glucan-mediated adherence in vitro or in vivo.