One of the pathogens of greatest concern to dentists and periodontists is Porphyromonas gingivalis (P. gingivalis). This pathogen is considered the primary etiological agent of periodontitis and it tricks human cells into taking control of them, thus creating the conditions for the progression of periodontitis.
Dr. Mary Ellen Davey, Professor at the ADA Forsyth Research Institute, has dedicated more than a decade of her career to studying this pathogen and its interactions in the oral microbiome.
Dr. Davey is particularly interested in the effects of arginine on Porphyromonas. Arginine is an amino acid that helps the body synthesize proteins. It is also essential for the immune system to fight infection. Therefore, many pathogens use arginine to establish themselves in their human hosts.
While many oral bacteria live on arginine, Porphyromonas does not consume arginine for energy, but instead converts it into a variety of metabolites.
“It was curious why P. gingivalis was so focused on this particular amino acid,” said Dr. David.
Funded by an NIH R01 grant, Dr. David’s current research shows that arginine influences P. gingivalis colonization and survival within the gums.
The work of ADA Forsyth scientists on this topic furthers our understanding of P. gingivalis and periodontitis. By expanding our understanding of the signals that guide oral pathogens to colonize, scientists can uncover new avenues for therapeutic strategies.
In exploring these signals, the researchers found that varying levels of arginine in the microbial ecosystem can be both beneficial and detrimental to P. gingivalis. When arginine concentrations are high, it is toxic to P. gingivalis. The pathogen forms a biofilm to cope with adverse conditions and survive.
When P. gingivalis proteases break down proteins, arginine is introduced to the oral microbiome, which is then used by other bacteria for growth. In fact, arginine is a preferred energy source for many bacteria. Essentially, the waste products of one bacterium cause specific responses in other bacteria in the ecosystem.
“I think this is a perfect example of how bacteria are interconnected within communities,” Dr. David said. “The end product is produced by one organism, and another organism provides nutrients for it.”
While Dr. David focuses on the microbiology in subgingival tissue, where P. gingivalis primarily lives, the importance of arginine above the gums is well established.
Arginine is used in toothpaste to treat tooth sensitivity, but it also affects oral Streptococcus and raises oral pH, helping to prevent tooth decay. The fact that arginine is an important amino acid in the mouth made Dr. David very interested in the role of arginine below the gum line.
“It was known that arginine was a very important substrate, but no one had really studied it in the context of the subgingival microbiome, so we were trying to connect the two systems,” said Dr. David. “The ecological aspect of this study really helped us understand the importance of this substrate.”
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