The isolation of Streptococcus mutans mutational phase III-like organisms from human dental plaque

Abstract

Mutational phase III induced from Str. mutans by means of a mutagen lack in its cariogenicity. Moreover, phase III strains showed a caries-inhibitory effect when they were inoculated into the oral cavity of experimental animals. The purpose of this study was to isolate Str. mutans mutational phaseIII-like organisms from human dental plaque.
Human dental plaque was collected from 204 infants and 109 adults. Plaque samples were smeared on TYC Agar and MS Agar plate. After incubation, colonies which resembled phase III strains were selected from both agar plates, and were subjected to the slide agglutination test using specific antisera against group H Str. mutans. Nine strains showed positive reaction against those sera, and were isolated.
The characteristics of these nine strains were investigated with the following tests; mesurement of agglutination titer against anti-H group Str. mutans serum, bicchemical behaviour, plaque formation on the glass of the test tube, ouchterlonly test, and mesurement of glucosyltansferase activity.
A few representative strains were examined for cariogenic activity in golden hamsters. All nine strains showed very similar behaviour in the tests, and there were much resemblance between them and Str. mutans mutational phase III strains. The tested strains induced no cariesin hamsters.
Consequently, it was concluded that organisms which resemble Str. mutans mutational phase III strains might exist in human dental plaque.