Genotypic heterogeneity of Streptococcus oralis and distinct aciduric subpopulations in human dental plaque

The genotypic heterogeneity of Streptococcus oralis isolated from the oral cavity was investigated using repetitive extragenic palindromic PCR. Unrela ted subjects harbored unique genotypes, with numerous genotypes being isola ted from an individual. S, oralis is the predominant aciduric bacterium iso lated from non-carious tooth sites. Genotypic comparison of the aciduric po pulations isolated at pH 5.2 with those isolated from mitis-salivarius agar (MSA) (pH 7.0) indicated that the aciduric populations were genotypically distinct in the majority of subjects (chi(2) = 13.09; P = 0.0031). Neither the aciduric nor the MSA-isolated strains were stable, with no strains isol ated at baseline being isolated 4 or 12 weeks later in the majority of subj ects. The basis of this instability is unknown but is similar to that repor ted for Streptococcus mitis. Examination of S. oralis strains isolated from cohabiting couples demonstrated that in three of five couples, genotypical ly identical strains were isolated from both partners and this was confirme d by using Salmonella enteritidis repetitive element PCR and enterobacteria l PCR typing. These data provide further evidence of the physiological and genotypic heterogeneity of non-mutans streptococci. The demonstration of di stinct aciduric populations of S. oralis implies that the role of these and either non-mutans streptococci in the caries process requires reevaluation .