Although substantial epidemiologic evidence links Streptococcus mutans to caries, the pathobiology of caries may involve more complex communities of bacterial species. Molecular methods for bacterial identification and enumeration now make it possible to more precisely study the microbiota associated with dental caries. The purpose of this study was to compare the bacteria found in early childhood caries (ECC) to those found in caries-free children by using molecular identification methods. Cloning and sequencing of bacterial 16S ribosomal DNAs from a healthy subject and a subject with ECC were used for identification of novel species or uncultivated phylotypes and species not previously associated with dental caries. Ten novel phylotypes were identified. A number of species or phylotypes that may play a role in health or disease were identified and warrant further investigation. In addition, quantitative measurements for 23 previously known bacterial species or species groups were obtained by a reverse capture checkerboard assay for 30 subjects with caries and 30 healthy controls. Significant differences were observed for nine species: S. sanguinis was associated with health and, in order of decreasing cell numbers, Actinomyces gerencseriae, Bifidobacterium, S. mutans, Veillonella, S. salivarius, S. constellatus, S. parasanguinis, and Lactobacillus fermentum were associated with caries. These data suggest that A. gerencseriae and other Actinomyces species may play an important role in caries initiation and that a novel Bifidobacterium may be a major pathogen in deep caries. Further investigation could lead to the identification of targets for biological interventions in the caries process and thereby contribute to improved prevention of and treatment for this significant public health problem.

Periodontitis is a common, progressive disease that eventually affects the majority of the population. The local destruction of periodontitis is believed to result from a bacterial infection of the gingival sulcus, and several clinical studies have provided evidence to implicate Porphyromonas gingivalis. If P. gingivalis is a periodontal pathogen, it would be expected to be present in most subjects with disease and rarely detected in subjects with good periodontal health. However, in most previous studies, P. gingivalis has not been detected in the majority of subjects with disease, and age-matched, periodontally healthy controls were not included for comparison. The purpose of the study reported here was to compare the prevalence of P. gingivalis in a group with periodontitis to that of a group that is periodontally healthy. A comprehensive sampling strategy and a sensitive PCR assay were used to maximize the likelihood of detection. The target sequence for P. gingivalis-specific amplification was the transcribed spacer region within the ribosomal operon. P. gingivalis was detected in only 25% (46 of 181) of the healthy subjects but was detected in 79% (103 of 130) of the periodontitis group (P < 0.0001). The odds ratio for being infected with P. gingivalis was 11.2 times greater in the periodontitis group than in the healthy group (95% confidence interval, 6.5 to 19.2). These data implicate P. gingivalisin the pathogenesis of periodontitis and suggest that P. gingivalis may not be a normal inhabitant of a periodontally healthy dentition.

To determine if there is variability in virulence among strains ofPorphyromonas gingivalis in human periodontitis, their distribution in a group of subjects with clear indicators of periodontitis and in a healthy, age-matched control group was examined. The presence of heteroduplex types of P. gingivalis in the two groups was determined with a PCR-based assay. This assay relied on detection of polymorphisms in the ribosomal internal spacer region (ISR). ISR fragments generated by PCR with P. gingivalis-specific primers were hybridized to fragments from reference strains, and the formation of heteroduplexes from the hybridization of nonidentical sequences was observed by polyacrylamide gel electrophoresis. Characteristic fingerprints from comparison with a panel of reference strains allowed the identification of heteroduplex types in clinical samples. One hundred thirty adults with periodontitis and 181 controls were sampled. With this approach, 11 heteroduplex types of P. gingivalis were detected in the population. Sufficient numbers were available for statistical analysis of six of these types. Heteroduplex type hW83 was found to be very strongly associated with periodontitis (P = 0.0000), and two additional types, h49417 and hHG1691, were also significantly associated with disease. The remaining types, h23A4, h381, and hA7A1, were detected more frequently in subjects with periodontitis than in healthy subjects, but the difference was not significant. These data indicate that virulence in human periodontitis varies among strains ofP. gingivalis, and they identify an apparently highly virulent subgroup.