One of the most notorious pathogens on the radars of dentists and periodontists is Porphyromonas gingivalis, or P. gingivalis. This pathogen, known as a major agent of periodontitis, tricks human cells, taking them over to create conditions that allow periodontitis to progress.
Mary Ellen Davey, Professor at the ADA Forsyth Institute, has dedicated over a decade of her career exploring this pathogen and its interactions within the oral microbiome.
In particular, Dr. Davey has been studying the impact of arginine on Porphyromonas. Arginine is an amino acid that helps the body build proteins. It is also critical for the immune system to fight off infections. For this reason, it is manipulated by many pathogens to gain a foothold in their human host.
It’s sort of a curiosity as to why P. gingivalis has so much of a focus on this particular amino acid
Mary Ellen Davey, PhD
While many oral bacteria grow on arginine, Porphyromonas does not consume arginine to gain energy. Instead, it converts it to a variety of metabolites.
“It’s sort of a curiosity as to why P. gingivalis has so much of a focus on this particular amino acid,” Dr. Davey said.
Funded by an R01 grant from the National Institutes of Health, Dr. Davey’s current study shows that arginine influences colonization and survival of P. gingivalis within the gums.
The findings by scientists at ADA Forsyth on this topic further develop our understanding of P. gingivalis and periodontitis. By expanding our understanding of the signals that guide colonization of oral pathogens, scientists can discover new pathways toward therapeutic strategies.
While exploring these signals, researchers found that differing levels of arginine in the microbial ecosystem can be either beneficial or toxic to P. gingivalis. When arginine is at high concentration, it is toxic to P. gingivalis. The pathogen creates a biofilm to stay alive in response to adverse conditions.
Arginine is introduced to the oral microbiome when proteins are broken down by P. gingivalis proteases and then other bacteria use the arginine to grow. In fact, arginine is a preferred energy source for many bacteria. In essence, one bacterium’s waste product leads to a specific reaction by other bacteria in the ecosystem.
“I think it’s a perfect example of how interconnected the bacteria are within the community,” Dr. Davey said. “End products are made by one organism that feed another organism.”
While Davey focuses on microbiology in the subgingival tissue, where P. gingivalis primarily lives, the significance of arginine above the gums has been well established.
Arginine is used in toothpaste to treat sensitivity, but it also influences oral streptococci, raising the pH level in the mouth and assisting in prevention of cavities. The fact that arginine is an important amino acid throughout the oral cavity intrigues Dr. Davey as she discovers more about its role below the gumline.
“It’s known that arginine is a really important substrate, but nobody’s really studied it in the context of the subgingival microbiome, so we’re trying to tie the two systems together,” Dr. Davey said. “The ecological aspects of this research have really helped us understand how important this substrate is.”
