Microbial Complexes in Subgingival Biofilm

Bacterial complexes as described by Socransky et al.

In 1968 Sigmund Socransky classified the bacterial species involved in the initiation and progression of periodontal disease. He classified several complexes of bacteria dividing them in groups, labeled by colors. The categories were based upon the pathogenicity of the bacteria and their role in the development of plaque (a bacterial microfilm). The red complex and the individual species in that group were also strongly associated with bleeding on probing.

The red complex is a group of bacteria that are categorized together based on their association with severe forms of periodontal disease. The three members of the red complex are:

Species in the red complex exhibited a very strong relationship with pocket depth. Sites with none of the species exhibited the shallowest mean pocket depth, while sites harboring all 3 showed the deepest. It is interesting to note that sites harboring P. gingivalis alone or in combination with the other 2 species exhibited the deepest mean pocket depths.

The red complex showed the strongest relationship with the clinical parameters considered most meaningful in periodontal diagnosis.

The orange complex is constituted by:

  • Fusobacterium nucleatum
  • Prevotella intermedia
  • Prevotella nigrescens
  • Peptostreptococcus micros
  • Streptococcus constellatus
  • Eubacterium nodatum 
  • Campylobacter showae
  • Campylobacter gracilis
  • Campylobacter rectus

The species in this group were closely associated with one another and this complex appeared closely related to the red complex. Ali et al. (1994) found that P. intermedia was always detected in the presence of F. nucleatum in subgingival plaque samples from deep pockets in a group of adult periodontitis subjects. Similarly to the red complex, all species in the orange complex showed a significant association with increasing pocket depth. Further, treatment that included systemically administered metronidazole decreased levels of these species and improved periodontal status.

The yellow complex is constituted by:

  • Streptococcus sanguis
  • Streptococcus oralis
  • Streptococcus mitis
  • Streptococcus gordonii
  • Streptococcus intermedius
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42 responses to “Microbial Complexes in Subgingival Biofilm

  1. Hi, do you know why Aggregatibacter actinomycetemcomitans is only categorised in the green group? I thought it was particularly virulent in regards to periodontal disease?

    • Because the association with loss of attachment and presence of AA in patient with chronic periodontitis is not very strong.
      AA is definitely an important bacteria in the onset and progression of periodontal disease but recently also other bacteria have been associated with aggressive forms of periodontal disease, such as porphyromonas gingivalis (usually associate to chronic perio) and also certain viruses!

    • Thank you for your question.
      While the Socransky 1998 is a very important publication (another landmark) his original research started three decades before, in 1968.

      Predominant cultivable micro-organisms inhabiting periodontal pockets. Dwyer DM, Socransky SS. Br Dent J. 1968

      • I am doing a research about the history of the periodontal pathongens’ classification. Can you help me understand the differences between the 1968 Classification and the one published in 1998? Thank you.

      • Sure I can help.
        Most of changes in the classification are due to the development of new investigative techniques. For example in 1968 the most common way of analyzing bacteria was dark field microscopy, that was surpassed by newer technologies in 1998 (including new instruments such as DNA analysis).
        Also in 1998 there was more clinical research linking certain bacterial strains to clinical signs of periodontal disease, therefore some of the bacteria changed group.

    • Hi Nour,
      Bacteria from the yellow complex have not been directly associated with changes in clinical signs of periodontal disease (such as bleeding on probing, probing pocket depth, and clinical attachment level).

    • Some of these bacteria are part of the regular flora of the mouth. Others are acquired by vertical (i.e. mother to son) or horizontal (peer to peer) transmission. The periodontal pocket constitutes a very fertile ground for these bacteria. Most of them a GRAM- anaerobic. This means that they proliferate and thrive in an environment deprived of oxygen (like a periodontal pocket).
      Each bacteria taken individually might not be as pathogenic as when they form a complex.

    • Here are some of the antibiotics most commonly used for the treatment of periodontal disease
      – Amoxicillin
      – Amoxicillin + Metronidazole
      – Amoxicillin + Clavulanic Acid (Augmentin)
      – Doxycyclin
      – Clindamycin
      or combinations of the above.

    • I do not know about the indigo complex. Maybe was the purple complex?
      There are so many bacterial complex colonizing the periodontal space, that I would not be surprised if “new” bacteria were discovered and classified in the indigo complex.

    • The purple complex is among the first ones to colonize the subgingival sulcus, however it is not directly associated with gingivitis or periodontitis.
      Basically, it seems to pave the way for the other bacterial complexes. It is frequently found in combination with the Actinomyces species.

  2. Hello,
    I know that A. Actinomycetemcomitans has been reclassified in 2008 and now is part of the red complex,do you know anything about?

    • I Knew it changed name, from Actinobacillus to Aggregatibacter but I did not know it changed group. Do you have a reference for that? I would be interested in reading more about it.I assume there has been a series of clinical investigations linking AA to loss of attachment…

    • They are all linked to gingivitis. It comes down to what definition of gingivitis you are using as well as Negative and Positive Predictive Value.
      Just because you have one bacteria it does not mean you have gingivitis. And once you are diagnoses with gingivitis it does not mean you have that (or those) specific bacteria.
      Also consider that gingivitis (defined as histological presence of inflammatory infiltrate without loss of attachment) is pretty much universal.
      So I would consider some confounding factors such as: water fluoridation (and in general condition of drinking water), diet, oral hygiene regimens, tooth brushing trauma, systemic health, pharmacological therapy, social habits (smoking, alcohol, betel nut, etc), presence of dental restorations, and many other; very important in the establishment of a specific flora.

  3. what is the complex that lead to gingivitis? and what micro-organism initiate periodontal plaque
    please answer because i’m confused
    am read this artical but also confused

    • the first bacteria to attach to the pellicle are: S.Gordoni, S. Sanguis, S. Oralis. Those belong to the yellow group.
      I don’t see yellow among the answer.
      If those are your options I would probably go by exclusion. Black does not exist, purple is a very rare group. So you are left with Red and Orange. Red is specific for loss of attachment (periodontal disease), and question asks about gingivitis, not periodontitis (defined as loss of attachment). Orange contains a wide spectrum of bacteria. I would probably for with orange.

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