EMERGENCE IN HUMAN DENTAL PLAQUE AND HOST DISTRIBUTION OF AMYLASE-BINDING STREPTOCOCCI

Salivary amylase is known to bind specifically to several species of o ral streptococci. To assess the importance of this interaction in bact erial colonization of the oral cavity, we determined the proportion an d identity of amylase-binding bacteria (ABB) in dental plaque of human s and various salivary amylase-secreting and non-secreting mammalian s pecies. The numbers of ABB in undisturbed plaque collected over time f rom tooth surfaces of six human volunteers or from 14 other mammalian species were determined by means of a replica-plating assay. The mean proportion of ABB cultured aerobically from human teeth at 2 h was 10. 5% (SD 10), at 8 h 7.9% (8), at 24 h 13% (11), and at 48 h 12% (9). Th e mean proportion of anaerobically cultured ABB found at 2 h was 3% (S D 4), at 8 h 5% (5), at 24 h 12% (9), and at 48 h 16% (12). Amylase-bi nding bacteria cultured from these samples resembled Streptococcus mit is, Streptococcus gordonii, Streptococcus salivarius, Streptococcus cr ista, or unidentified streptococci. In addition, only animals exhibiti ng salivary amylase activity in their saliva harbored ABB (ranging fro m 2 to 31% of the total flora), with the exception of the pig, where n o ABB were found to colonize, despite considerable amylase activity in saliva. Only strains resembling S. mitis and S. salivarius and unspec iated strains were isolated from these mammals. These results suggest that amylase-binding streptococci are the predominant ABB in human pla que, and their numbers generally increase as plaque develops. Since AB B colonized only the oral cavities of hosts demonstrating salivary amy lase activity, the ability to bind amylase may play an important role in oral colonization by these bacteria.