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J Bacteriol. 1971 April; 106(1): 192-196
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Genetic Heterogeneity in Streptococcus mutans¹

^a Department of Microbiology, Naval Medical Research Institute, Bethesda, Maryland 20014

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 (¹⁴C-DNA) was extracted from strains 10449, FAl, and SLl. Denatured ¹⁴C-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 ¹⁴C-DNA reassociated extensively only with GS5 and Ingbritt DNA. FAl ¹⁴C-DNA hybridized extensively only with BHT DNA, and SLl ¹⁴C-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 ¹⁴C-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.

¹ From the Bureau of Medicine and Surgery, Department of the Navy, Research Task MR005.05.01-0015A3JJ.

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