Isolation of dextranase-producing microorganisms from human early dental plaque and their effects on sucrose-dependent in vitro plaque formation.

Dextranase-producing microorganisms were isolated from the dental plaque formed in 3 hr on the cleaned buccal surface of the maxillary molars of adult volunteers by the Blue Dextran agar plate method. Dextranase producers were detected in 5 of 8 plaque samples and their proportion varied ranging up to 2.57% of the total number of colonies recovered. Three representative isolates possessing higher dextranase activity were tentatively identified as Streptococcus mitis. Cells of the isolates agglutinated upon addition of human whole saliva supernatant and were adsorbed on uncoated and saliva-coated hydroxyapatites. In the mixed culture with a Streptococcus mutans strain in sucrose broth, two of the isolates inhibited the sucrose-dependent strong adherence of S. mutans cells on glass and enamel slabs, whereas one isolate did not affect the cellular adherence. The in vivo role (s) of the dextranase-producing plaque flora is discussed with respect to the establishment and persistence of cariogenic S. mutans on tooth surfaces.