Isolation and characterization of mutants of Streptococcus mutans K1-R

Abstract

The purpose of this study was to isolate mutants of S. mutans strain K1-R with nitrosoguanizine. Thirty-eight mutants were isolated in colonial morphology, and their polysaccharide synthesis, adherence, agglutination, growth and fermentation were compared with these of the parent strain. A correlation was observed between the adhesive ability on glass and the ratio of cell-associated glucan to total glucan synthesized. The percentage of cell-associated glucan to the total varied from 1 to 79 among the strain of mutants. An adhesive translucent granule was observed on the glass when the ratio of cell associated glucan to the total glucan decreased to less than 20%. Adherence was unobserved in mutants with less than 1%. The ability of agglutination was not significantly affected to the degree of adherence on the glass. Hamsters, which had received cariogenic diet #2000, were orally inoculated with a strain of mutants, and the caries score was compared among the mutants. The results suggest that the cell-associated glucan is not the sole factor for the caries incidence, and other factors of the strain might be involved to develop the lesion. Actually, the caries score decreased by 61% of that of the parent with an inoculation of mutant M38, which produced highly cell-associated glucan. Mutant Ml could also be established on the teeth to the same proportion as the parent, but the score decreased by 77%. The results suggested that a high cariogenic plaque flora may be modified to a low cariogenic one using the mutants with a higher adhesive and lower cariogenicity.