Classification of Periodontal Bacteria

Periodontal disease results from complex interactions between etiologic agents and host tissues. Because there are numerous etiologic causes of periodontitis, it is often times difficult to determine. There are many factors both local and systemic which influence the course of disease by modifying the processes in the bacterial host interaction.

Factors such as inflammation, the host response to bacterial plaque, individual genotype, environmental influences, and systemic disease make it impossible to individually rule out a single etiologic cause of periodontal disease. As a result, numerous hypotheses were developed in order to classify and group bacteria. One such grouping was developed by Socransky and is based upon cluster analysis and community ordination.

Subgingival plaque samples were taken from the mesial aspect of each tooth in 185 subjects with and without periodontitis. The presence and levels of 40 subgingival taxa were determined in 13,261 plaque samples using whole genomic DNA probes and DNA hybridization. Clinical assessments were made at 6 sites per tooth at each visit. Community ordination was performed and 5 major complexes were consistently observed using any of the analytical methods. One complex (red) consisted of tightly related groups: B Forsythus, P Gingivalis, and T Denticola.

The 2nd complex (orange) consisted of a tightly related core group including members of the F Nucleatum, P intermedius, P nigrescens, and P micros. The 3rd complex (yellow) consisted of S Sanguis, S oralis, S mitis, S gordonii and S intermedius. The 4th complex (green) was comprised of Capnocytophagia, C concius, E corrodens and A Actinomycetemcomitans. The 5th complex (purple) consisted of V parvula, A odontolyticus, A actinomycetemcomitans, S noxia and A naeslundii. The 1st complex related strikingly to clinical measures of periodontal disease particularly pocket depth and bleeding upon probing.

The significance of these groupings are due to the relationship of these bacteria in periodontal disease. For example P.gingivalis, T denticola, and B forsythus (red complex) are more frequently found in higher numbers in deeper periodontal pockets. In addition, P gingivalis was never found without B forsythus. The orange complex also reveals a similar pattern to that of the red complex. In a group of periodontal patients, P intermedia was always found in the presence of F nucleatum. P micros and C rectus were significantly elevated in samples from mobile teeth compared with non-mobile teeth.

Knowledge of the associations between the subgingival species can be used to aid in periodontal treatment planning. For instance, the recognition that the inter-related influence of the red complex suggests that therapies that affect one bacteria in this complex may affect the colonization of this group. In addition, it can be speculated that altering the orange complex could have an adverse affect on the red complex.

In addition, the treatment of certain pathogens (A actinomycetemcomitans) could have no affect against other bacteria in other complexes for instance in the case of scaling and root planing. Knowledge of these groupings can aid in periodontal treatment planning and thus allow for a better approach by dental therapists.