Isolation and some properties of extracellular glucan-producing strains of human oral Streptococcus salivarius.

A total of eighteen strains of Streptococcus salivarius, which formed rough gelatinous, rough mucoid or smooth mucoid colonies on sucrose agar media, were isolated from the saliva and tongue dorsum of adults. All of the isolates produced glucans as well as fructans from sucrose. The bulk of the glucans was synthesized by the extracellular enzyme fraction and was water insoluble, whereas most of the fructans were synthesized by the cell-associated enzyme fraction and were water soluble. All strains formed microbial deposits on wire and glass surfaces when cultured in sucrose broth, but their sucrose-dependent adhesion was apparently looser than that produced by a cariogenic S. sobrinus strain. The rough gelatinous colony forming strains possessed a greater ability to synthesize water-insoluble glucans and produced heavier deposits with higher cohesion. Preliminary studies showed that the S. salivarius of such characteristic forms of colony were detected primarily in the saliva and tongue dorsum: the smooth mucoid colony formers appeared to predominate in the tongue coat and the rough mucoid and rough gelatinous colony formers were prominent in saliva. Isolation of these S. salivarius from dental plaques was low.