Genetic Heterogeneity in Streptococcus mutans

Abstract

The genetic homogeneity among eight cariogenic strains of Streptococcus mutans was assessed by deoxyribonucleic acid (DNA)-DNA reassociation experiments. DNA species were extracted from strains GS5, Ingbritt, 10449, FAl, BHT, E49, SLl, and KlR. Labeled DNA ( 14 C-DNA) was extracted from strains 10449, FAl, and SLl. Denatured 14 C-DNA fragments were allowed to reassociate, i.e., form hybrid duplexes, with denatured DNA immobilized on membrane filters incubated in 0.45 m NaCl-0.045 m sodium citrate at 67 or 75 C. At 67 C, 10449 14 C-DNA reassociated extensively only with GS5 and Ingbritt DNA. FAl 14 C-DNA hybridized extensively only with BHT DNA, and SLl 14 C-DNA reassociated with KlR and E49 DNA. DNA which hybridized extensively at 67 C also reassociated to a high degree at 75 C. Thermal elution of 14 C-FAl-BHT duplexes showed that the hybrid duplexes were thermostable. The results indicate that S. mutans is a genetically heterogeneous species. The strains studied can be divided into three (possibly four) genetic groups, and these groups closely parallel antigenic groups.