Microbiome study and gum disease

The human body is full of good bacteria. However, some of these microorganisms, like Veillonella parvula, can be too nice. These peaceful bacteria have a one-sided relationship with the pathogen Porphyromonas gingivalis, helping the germ to multiply and cause gum disease, according to a new study led by the University at Buffalo (United States).

Research has sought to understand how P. gingivalis colonizes the mouth. The pathogen is unable to produce its own growth molecules until it reaches a significant population in the oral microbiome (the community of microorganisms that live on and in the body).

The answer: It borrows growth molecules from V. parvula, a common but harmless bacteria in the mouth whose growth does not depend on population.

In a healthy mouth, P. gingivalis constitutes a tiny amount of bacteria in the oral microbiome and cannot reproduce. But if plaque is allowed to grow unchecked due to poor oral hygiene, V. parvula will multiply and eventually produce enough growth molecules to stimulate the reproduction of P. gingivalis as well.

More than 47% of adults ages 30 and older have some form of periodontitis (also known as gum disease), according to the Centers for Disease Control and Prevention. Understanding the relationship between P. gingivalis and V. parvula will help researchers create targeted therapies for periodontitis, say the US researchers.

"Having worked with P. gingivalis for nearly two decades, We knew that it needed a large population size to thrive, but the specific processes that caused this were not completely understood," according to these researchers. "Successfully targeting the accessory pathogen V. parvula should prevent P. gingivalis from spreading within the oral microbial community to pathogenic levels," they added.

L The study, which was published Dec. 28 in the journal ISME, tested the effects of growth molecules exuded by microorganisms in the mouth on P. gingivalis, including molecules from five species of bacteria that are prevalent in gingivitis , a condition that precedes periodontitis.

Of the bacteria examined, only growth molecules secreted by V. parvula allowed replication of P. gingivalis, regardless of the strain of either another microbe. When the researchers removed V. parvula from the microbiome, the growth of P. gingivalis stopped. However, the mere presence of V. parvula was not enough to stimulate P. gingivalis, as the pathogen was only stimulated by a large population of V. parvula.

The data suggest that the relationship is unidirectional, because V. parvula received no obvious benefit from sharing its growth molecules, according to the study leader.

"P. gingivalis andV. parvula interact on many levels, but the beneficiary is P. gingivalis."

"This relationship that allows the growth of P. gingivalis has not only been confirmed in a preclinical model of periodontitis, but also, in the presence of V. parvula, P. gingivalis could amplify periodontal bone loss, which is the hallmark of the disease," said another researcher from the University of Pennsylvania.

Finally, The study states that it is unclear whether the growth signals produced by P. gingivalis and V. parvula are chemically identical, and that much work is still needed to discover the precise identity of these molecules.