Research from the University of Florida College of Dentistry examines how a genetic mechanism inside Porphyromonas gingivalis regulates the bacterium’s virulence and may inform future approaches to treating periodontal disease without disrupting beneficial oral microbes.
The study, led by oral biologist Jorge Frias-Lopez, Ph.D., investigated a CRISPR array within P. gingivalis, a bacterium considered a keystone pathogen in periodontal disease. Even at low levels, the organism can alter the oral microbial community in ways that promote disease.
Periodontal disease affects about 42% of people over age 30 in the United States and is a common cause of tooth loss due to destruction of the bone supporting the teeth. The condition also carries significant economic impact, with losses exceeding $150 billion annually in the United States, largely due to missed work and treatment needs.
The researchers examined a section of the bacterium’s genome known as CRISPR array 30.1. CRISPR systems function as bacterial immune defenses by storing fragments of viral DNA, called spacers, which help bacteria recognize and destroy viruses during subsequent attacks.
However, the spacers in CRISPR array 30.1 did not match known viral sequences. Such sequences are sometimes described by scientists as CRISPR “dark matter” or “orphan arrays” because their targets are unknown.
The team found that the spacers in this array matched the bacterium’s own DNA. To investigate the function of the array, researchers used gene editing to delete it from the genome of P. gingivalis.
The modified bacterium showed increased virulence compared with the normal strain. Without the array, P. gingivalis produced approximately twice as much biofilm. In host tests, the altered strain killed half the hosts in 130 hours, compared with 200 hours for the normal strain. The modified strain also triggered stronger inflammatory responses in human immune cells.
The findings suggest the CRISPR array functions as a regulatory mechanism that limits the bacterium’s aggression. By restraining its virulence, P. gingivalis can remain in the gingival environment without triggering a strong immune response, contributing to chronic infection.
Current periodontal therapies commonly include subgingival debridement, removal of diseased tissue, or antibiotics. While these approaches reduce bacterial load, they also affect beneficial members of the oral microbiome and may contribute to antibiotic resistance.
The study points to the possibility of therapies designed to target P. gingivalis specifically. One concept described by the researchers involves engineered bacteriophages that could deliver CRISPR instructions to the pathogen, locking the regulatory mechanism in place and reducing virulence while preserving the broader microbial community.
The research also has potential relevance beyond oral health. Periodontal disease has been associated with systemic conditions such as heart disease and diabetes. Studies indicate that in more than half of periodontal disease patients, bacterial toxins from inflamed gum tissue enter the bloodstream and circulate to other organs, contributing to inflammation elsewhere in the body.
By controlling the behavior of P. gingivalis, targeted therapies could influence both periodontal disease progression and the systemic inflammatory effects associated with the condition.
