Association between Bifidobacteriaceae and the clinical severity of root caries lesions

The isolation of members of the family Bifidobacteriaceae (bifids) from oral samples has been sporadic and a recent cloning study has suggested that they are not detectable in root caries lesions. To better understand the presence of bifids in root caries we obtained clinical samples (15 of each) from sound exposed root surfaces, leathery remineralizing root lesions, and soft active root lesions. We investigated each for the presence of bifids using a mupirocin-containing selective medium and identified the isolates using 16S recombinant RNA sequencing. The proportion of bifids, as a percentage of the total anaerobic count, was significantly related to the clinical status of the sites sampled, being 7.88 +/- 1.93 in the infected dentine from soft lesions, 1.61 +/- 0.91 in leathery lesions, and 0.05 +/- 0.39 in plaque from sound exposed root surfaces. Bifids were isolated from all soft lesions, 13 of 15 leathery lesions, and five of the plaque samples. Bifidobacterium dentium was isolated from four of the plaque samples, from 13 samples from leathery lesions, and from 12 of the 15 samples of infected dentine from the soft active lesions. Parascardovia denticolens and Scardovia genomospecies C1 were each isolated from samples associated with all three clinical conditions whereas Scardovia inopicata and Bifidobacterium subtile were both isolated from the infected dentine of the leathery and soft lesions. Bifidobacterium breve was isolated from the infected dentine of soft root caries lesions. Bifids may be routinely isolated from root caries lesions using appropriate cultural methods.