Mice Help Explain the Mystery of Bacterium’s Role in Periodontitis

Up until recently it has been a bit of a mystery as to how common oral bacteria such as P. gingivalis, A. actinomycetemcomitans, and T. fosythia, were able to wreak such havoc in the mouth. Scientists have pondered for years how exactly they were able to trigger periodontitis, despite being present in relatively low numbers in the sub gingival crevice. Now researchers have discovered that the common oral bacteria P. gingivalis is able to reprogram the immune cells that normally protect the sub gingival crevice, into creating conditions it finds more favourable.

The reprogrammed immune cells effectively persuade more immune cells to follow their lead, prompting the usually benign bacterial residents of the sub gingival crevice to rise up and defend their realm, which in turn leads to inflammation of the supportive structures of the tooth. Prior to this research it had often been thought that P. gingivalis was directly responsible for the infection, but it now seems likely that it just sits back to watch the destruction unfold, waiting to feed off the nutrients generated by the inflammation.

George Hajishengallis, D.D.S., Ph.D., a researcher at the University of Louisville School of Dentistry was a co-lead author on the study which was supported by the National Institute of Dental and Craniofacial Research, and has commented that this research is important as it is the first documented case of a keystone species being discovered in microbiology. The term keystone species was first invented in the late 1960s and is a species which is present in low numbers but which is able to exert a disproportionate influence on its environment. P. gingivalis, a common oral bacteria, would seem to be a perfect example as it is able to change the microbial environment creating conditions favourable for periodontitis to develop.

As yet it is still unknown if the bacterium behaves in the same way in people, but if it does it could affect the way periodontitis is treated. Before this research it had always been assumed that P. gingivalis used chemicals to defeat the immune cells, but scientists had always wondered exactly how this could happen when the bacterium appeared to be present in such low numbers. They had also wondered why mice when infected with P. gingivalis subsequently went on to develop high levels of normally benign bacteria in the infected periodontium, while levels of P. gingivalis remained difficult to detect. In contrast mice bred in a germfree environment remained resistant to periodontitis even after being infected with P. gingivalis. This new research explains a lot and it will be interesting to see what research on humans reveals.


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One Response to “Mice Help Explain the Mystery of Bacterium’s Role in Periodontitis”

  1. Thanks for linking to that interesting paper!

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