New Data Suggest Chronic Periodontitis Involves More Oral Bacteria Than Previously Thought
September 8, 2005
For most of the 20th century, scientists extracted plaque from periodontal infections, placed it in a culture dish, then looked for the known bacterial species. This research led to the paradigm that a small subset of bacteria in the mouth, most notably the so-called “gram-negative” bacteria such as Porphyromonas gingivalis, probably teamed up to cause periodontal disease. But, as molecular-based techniques to identify oral bacteria have matured in recent years, some scientists have proposed that a new paradigm might be in order. In the August issue of the Journal of Clinical Microbiology, a team of NIDCR grantees add important new data in support of this idea.
The scientists used open ended molecular based techniques - that is, cataloguing a broader array of the bacteria present, not just the known species - to compare the subgingival bacteria of a group of fifteen people in good oral health with another group of fifteen that had moderate to severe periodontitis. After identifying a total of 274 bacterial species in the samples, including six that were novel, the scientists found that 60 percent of these bacteria were from as yet uncultivated species, meaning studies a decade or more ago would have missed the bacteria completely. The group also assembled a distinct and unexpected bacterial profile between good oral health and periodontitis. Looking at the level of bacterial genera - clusters of related species - the researchers found several associations for both groups “among the gram positives rather than the gram negatives usually thought to be important in disease.” They also noted that several of the newly identified bacteria outnumbered P. gingivalis and other species traditionally thought to play a role in periodontal disease, although it was unclear whether novel and more numerous species may play a more important role in causing the condition. The authors also observed that, “. . . more differences were found in the bacterial profile of the two subject groups than between deep and shallow sites within the same mouth. This suggests that chronic periodontitis is the result of global perturbation of the oral bacterial ecology rather than a disease-site specific microbial shift.”