Differentiation of Streptococcus sobrinus and Streptococcus downei by DNA Hybridization

Abstract

Streptococcus sobrinus and Streptococcus downei are closely related cariogenic species. A DNA fragment (1.2 kb) of a central region of the S. sobrinus dextranase gene (dex) was amplified by polymerase chain reaction and utilized for a DNA probe to differentiate S. sobrinus and S. downei. The dex probe was dot-hybridized to the reference strains (17 strains of 5 species) of mutans streptococci and other related strains (13 strains of 9 species). The probe hybridized only to both S. sobrinus and S. downei at a highly stringent condition, but to none of the other mutans streptococci nor other gram-positive cocci. To differentiate S. sobrinus and S. downei, Southern blot hybridization was carried out against restriction fragments of chromosomal DNAs with the dex probe. The probe showed species-specific hybridization patterns to the EcoRI, EcoRV, HindIII and PvuII-fragments. This result suggests that hybridization analysis with the dex DNA probe is useful for the detection and differentiation of S. sobrinus and S. downei.