The bacterial complexes as described by Socransky

Periodontopathogenic bacteria are divided into complexes depending on their properties and pathogenicity. These complexes are closely interrelated and together create a suitable environment.

Early colonizers

The bacteria in the green and orange-associated complexes are able to adhere to the pellicle by means of fimbriae and thereby avoid being flushed out with the gingival crevicular fluid. These “early colonizers” thus form the basis for colonization of the sulcus with other periodontitis-associated bacteria. They are classified as moderately pathogenic. Purely mechanical therapy is sufficient to reduce numbers of these bacteria, depending on their concentrations.

Bridge species

The orange complex includes bacteria which, as “bridge species”, form a link between the early colonizers and the highly pathogenic bacteria of the red complex. The pathogenic potential of these marker bacteria is significantly increased as a result of the production of various toxins and enzymes. The bacteria from the orange complex are responsible for progressive attachment loss and an increase in pocket depth. Through their metabolism, these bacteria also create the living conditions for the strictly anaerobic bacteria of the red complex and their colonization of the sulcus.

Periodontitis-associated bacteria are categorized in complexes shown as differently colored parts of a pyramide

Climax community

The occurrence of bacteria of the red complex and the Aa-complex is characteristic of the final colonization phase which culminates in the development of a structured, stable bacterial community (climax community). Colonization with these bacteria which are significantly involved in the destruction of the periodontium, builds on the presence of the less pathogenic species mentioned above. The highly pathogenic marker bacteria species of the red complex and the Aa-complex then aggressively drive the destruction of the soft tissue and bone through the production of potent virulence factors. Their ability to penetrate tissue also makes treatment difficult, meaning that mechanical methods alone are often not sufficient.