Biochemical study of the relationship of extracellular glucan to adherence and cariogenicity in Streptococcus mutans and an extracellular polysaccharide mutant

Abstract

A mutant of S. mutans, GS-5, which differed in extracellular polysaccharide (EPS) produced from sucrose was used to study the role of EPS in the production of dental caries. The mutant proved to be identical to the parent strain in sugar fermentation, growth rate and serotype. Strain GS-5 synthesized an EPS, which in electron micrographs appeared to be of fibrillar structure, whereas the mutant produced no fibrillar material but only a globular EPS. Analysis of the EPS revealed that .apprx. 30% of the glucose units in the GS-5 polymer carried (1-3)-like bonds as branch points or as part of the linear backbone and that the mutant material contained only .apprx. 3% of these linkages. When grown in sucrose broth, the proportion of the mutant culture adherent to the glass vessel was dramatically less than that of the parent strain. Caries scores produced in conventional rats by the mutant were significantly lower than those obtained with the parent strain. Since the only difference discovered between strain GS-5 and the mutant was the inability of the mutant to synthesize a fibrillar EPS or an EPS with more than .apprx. 3% (1-3)-like linkages, the fibrillar EPS of strain GS-5 apparently contained .apprx. 30% (1-3)-like linkages and was necessary for adherence of the bacteria to surfaces and for production of dental caries in test animals.