Specificity of the oral microflora in dentinal caries, endodontic infections and periodontitis

The use of culture-independent molecular methods for the characterisation of the oral microflora in health and disease is revolutionising our understanding of the microbial ecology of the mouth. In addition, the use of 16S rRNA gene sequence analysis is allowing more precise identification of oral bacteria compared with that obtained using conventional phenotypic tests. The aim of this study was to use a combination of cultural and culture-independent methods to characterise the microflora in dentinal caries, endodontic lesions and periodontal pockets. Samples were cultured under aerobic and anaerobic conditions and randomly selected isolates were identified by 16S rRNA gene sequence analysis. In addition, DNA was extracted directly from the samples, 16S rRNA genes amplified by PCR and the amplified genes cloned to create Escherichia coli libraries. 3592 clones and isolates were sequenced and identified. 265 taxa, identified to species-level, were represented and belonging to 9 phyla: Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Fusobacteria, Proteobacteria, Spirochaetes, Synergistes and candidate Division TM7. 62 taxa were found in the endodontic samples, 98 in the carious lesions while the periodontal samples were the most species-rich with 161 taxa present. 15 taxa were found in both the caries and endodontic samples, 17 in the caries and periodontal samples and 21 in the endodontic and periodontal samples. Only 4 taxa were found in all three sample sets. In conclusion, the oral microflora is highly species-rich and the bacterial communities associated with the common dental diseases are specific to those diseases.