Abstract
After approximately 150 subcultures in the skimmed milk medium, we found a characteristically outstanding variant, designated as Streptococcus sp. 6480, from the parent strain Streptococcus NC 49, isolated previously from human dental plaque, lacking the ability to produce extra-cellular polysaccharides from sucrose.
Streptococcus sp. 6480 failed to produce acid from mannitol and sorbitol, whereas NC 49 as well as S. mutans produced it. The variant cells agglutinated slightly in anti-S. mutans serum but strongly in anti-Streptococcus sp. ATCC 15910 serum, though NC 49 cells agglutinated positively in anti-S. mutans NCTC 10449 serum.
Streptococcus sp. 6480 as well as its parent strain was not cariogenic in hamsters. When applied into the oral cavity of hamsters which were infected with S. mutans NCTC 10449, Streptococcus sp. 6480 significantly inhibited the induction of dental caries by S. mutans.
