The diversity and distribution of the predominant ribotypes of Actinomyces naeslundii genospecies 1 and 2 in samples from enamel and from healthy and carious root surfaces of teeth.

The bacterial communities associated with root caries are highly diverse and undergo succession during lesion formation. Consequently, root caries is said to have a polymicrobic etiology, typified by variation in the predominant species among samples from different lesions. Despite the polymicrobic etiology, A. naeslundii genospecies 1 and 2 (previously A. viscosus) have consistently been shown to be associated with root caries in humans; they predominate in some lesions and have been suggested to play a significant role in the disease. Several genetic variants of A. naeslundii are known to be present among the oral A. naeslundii population of an individual. The current study was initiated to explore the possibility that a variant in these A. naeslundii populations had characteristics which made it best fitted to colonize or promote root-surface caries lesions. Using ribotyping to detect variants, we tested the hypothesis that 'a ribotype of A. naeslundii best fitted to the environment would be selected and predominate in the A. naeslundii population of lesions'. Samples of plaque from enamel, normal root surfaces, plaque overlying the lesion, and material from within the lesion were taken from nine patients with soft root caries. The flora from 14 lesions and 9 enamel sites was analyzed on selective and non-selective media, and A. naeslundii genospecies were identified by serology. We ribotyped 972 isolates, showing 54 different patterns. Between 6 and 20 ribotypes were isolated from eight of nine patients. In general, each site from a patient showed a similar distribution of ribotypes. These results do not support the hypothesis and suggest that any phenotypic characters that allow A. naeslundii genospecies 1 and 2 to colonize or contribute to the formation of root-caries lesions are common among strains identified by ribotyping.