The microbiota of oral cavity is a
complex one. More than 700 species of organisms are present in the oral cavity
with every individual harbors atleast half of it. The role of red complex
bacteria, Aggregatibacter actinomycetemcomitans and virus in periodontitis had
been proved earlier. One more domain of organism constantly occurring in active
periodontitis sites is archaea, a methanogen. It utilizes metabolic products of
bacteria such as CO2, H2, acetate, formate etc and forms methane.
Methanobrevibacter oralis is the common methanogenic archaea isolated from
sites with chronic periodontitis, aggressive periodontitis and
peri-implantitis. Its prevalence was very low in healthy sites [1-3].
Methanogenic archaea are terminal degraders in periodontal pockets by removing
end products and H2, thus creating a favorable environment for anaerobes. Thus
they coexist with periodontal pathogens such as Capnocytophaga species,
Eubacterium nodatum, Streptococcus constellatus and proteolytic bacteria such
as Porphyromonas gingivalis and Tannerella forsythia [4]. Methanogenic archaea
transform metals or metalloids into more toxic volatile methylated derivatives,
which causes tissue damage [5]. Yamabe K et al demonstrated humoral immune
response to M. oralis [6]. de Lira EAG and Ramiro FS demonstrated reduction in
aggressive and chronic periodontitis patients by six months after Scaling and
root planning [7,8]. Archaea thus fulfils the first three criteria of Socransky
prostulate for a periodontal pathogen. No data are available for the capability
of methanogen to cause similar periodontal lesion in experimental animals. Even
though there are evidence about the role of methanogen in creating a favourable
environment for potential periodontal pathogen, no details are available
regarding the virulence factors. Data on humoral immune response to methanogen
was also inadequate. Existing data shows that methanogenic archaea play an
important role in the dark side of periodontitis but are inadequate and
inconclusive. Further studies with proper isolation techniques are needed to
conclude its definite role in the progression of periodontitis.