Methods: Root caries samples, collected from 45 patients, ranged in severity from healthy exposed dentine to soft active carious lesions. Occlusal samples from the deciduous dentition were collected from 5 caries free children and from occlusal caries in 23 children. Occlusal lesions were also sampled from 4 adult patients. Bifids were isolated on a mupirocin-containing medium and total anaerobic counts were determined using FAA medium. The identification of bifids was based on morphological and growth characteristics, detection of fructose-6-phosphate phosphoketolase and partial 16S rRNA sequencing and BLAST searching.
Results: A total of 979 bifids were identified and these included Bifidobacterium dentium, B. subtile, Parascardovia denticolens, Scardovia inopicata, S. genomosp. C1, B. breve. and B. longum. B. dentium was present in the majority of the samples and was the predominant species. Bifids formed 7.1 per cent of the cultivable flora from the active root caries lesions, 1.6 per cent from the leathery lesions and 0.06 per cent from the sound root surfaces (p<0.01) while from the occlusal lesions of the permanent dentition they formed 8.3 per cent and 7.4 per cent of the deciduous lesions. Bifids were isolated from all active root carious lesions and occlusal permanent carious lesions and not from the caries-free surfaces in the children.
Conclusion: The occurrence of the family Bifidobacteriaceae in dental caries was more complex than previously reported and there was an increased prevalence and proportion of bifids with root lesion severity. Bifids formed a significant proportion of the cultivable flora of root caries, deciduous and permanent occlusal caries lesions.
Supported in part by the Biomedical Research Centre of Guy's and St Thomas' Foundation Trust Hospital. Sample collection was approved by the local Ethics Committee.