OBJECTIVETo investigate the genotypic diversity of Actinomyces naeslundii in aged people and the relationship between the genotypes of Actinomyces naeslundii and root caries.

METHODSAccording to the inclusion criteria, 20 aged people with root caries and 20 without root caries were chosen into two groups for this study. Two sites were chosen in subjects with root caries: One site was the exposed sound root surface, and the other site was the root caries. In subjects without root caries the sampling site of root surface was exposed. Bacteria were cultured and then identified. Repetitive extragenic palindromic sequence-based polymerase chain reaction (REP-PCR) was used to analyze the genotypic diversity of the Actinomyces naeslundii clinic isolates.

RESULTS299 strains were isolated from the groups, 156 strains were chosen to analyze, belonged to 61 different genotypes. At the site of sound root surface in the subjects with root caries, there were 57 strains with 25 different patterns. At the site of root caries and of sound root surface in subjects without caries, there were 34 strains with 25 different patterns and 65 strains with 26 different patterns respectively. There was the genotypic diversity within Actinomyces naeslundii. There was significant difference in the genotypes in every individual site.

CONCLUSIONMany different genotypes of Actinomyces naeslundii concerned with occurrence of root caries.