Aggregatibacter actinomycetemcomitans (A.a.) is a specific type of bacterium that can reside in the human mouth. This small, non-motile, gram-negative rod is often a part of the normal oral microbiome. While it can exist without causing issues for some individuals, A.a. is also recognized as a significant pathogen. It belongs to the Pasteurellaceae family and is a facultative anaerobe, meaning it can grow with or without oxygen.
The Link to Gum Disease
Aggregatibacter actinomycetemcomitans has a strong association with Localized Aggressive Periodontitis (LAP), a severe form of gum disease frequently affecting younger individuals. This bacterium also plays a role in chronic periodontitis. It contributes to disease by invading the gum lining and releasing substances that destroy gum tissue and supporting bone around the teeth.
The bacterium possesses several virulence factors that enable its destructive actions. One factor is leukotoxin A (LtxA), a pore-forming toxin that directly targets and kills white blood cells, such as granulocytes and monocytes. This action helps A.a. evade the host’s immune response, allowing the infection to progress.
Another virulence factor is cytolethal distending toxin (CDT), which induces the expression of RANKL. RANKL then stimulates osteoclasts, cells responsible for breaking down bone, contributing to the bone loss seen in periodontitis. Uniquely among oral bacteria, A.a. produces both LtxA and CDT. Adhesins and fimbriae on the bacterial surface also allow A.a. to attach firmly to oral surfaces, promoting its colonization and persistence within the mouth.
Certain strains of A.a., particularly the serotype b JP2 genotype, are strongly linked to aggressive forms of periodontitis due to their high leukotoxin production. This genetic variation helps explain why some individuals develop more severe disease. These specific strains are of particular concern due to their enhanced ability to cause tissue damage and bone resorption.
Infections Beyond the Mouth
While Aggregatibacter actinomycetemcomitans is predominantly known for its role in gum disease, it can, in less common instances, travel through the bloodstream and lead to serious infections in other parts of the body. These systemic infections typically arise when the bacteria escapes the oral cavity, often in individuals with underlying health vulnerabilities or following invasive dental procedures.
Examples of these extra-oral infections include infective endocarditis, an infection of the heart lining and valves, and is the most frequently reported non-oral infection caused by A.a. The bacterium can also cause brain abscesses, which are collections of pus within the brain tissue. Bone infections, known as osteomyelitis, and pulmonary infections have also been documented. These complications are uncommon but represent severe health risks.
How The Bacteria Spreads
Aggregatibacter actinomycetemcomitans is primarily transmitted through saliva. Close personal contact can facilitate its spread among individuals. Transmission often occurs within families, such as from parent to child, a process referred to as vertical transmission. The bacterium can also spread horizontally between close contacts, including spouses.
While exposure to A.a. is common, not everyone who encounters the bacteria will develop gum disease or other infections. Many individuals can harbor A.a. as part of their oral flora without experiencing adverse effects.
Certain factors can increase the likelihood of exposure leading to disease. These include a genetic predisposition, which may make an individual more susceptible to the bacterium’s effects. A compromised immune system can also elevate the risk, as the body’s defenses may be less effective at controlling the bacterial population.
Detection and Medical Management
Detecting Aggregatibacter actinomycetemcomitans involves specific microbiological techniques. One traditional method is microbial culturing, where samples from periodontal pockets are grown on specialized agar plates.
Modern diagnostic approaches include Polymerase Chain Reaction (PCR) tests, which identify the bacterium by detecting its unique DNA sequences. PCR methods are often more sensitive and provide results more quickly than traditional culturing, offering a valuable tool for timely diagnosis. Combining both culturing and PCR methods can provide comprehensive detection.
Medical management of A.a.-associated infections involves a two-part treatment strategy. The first part is mechanical therapy, which includes professional dental cleanings such as scaling and root planing. These procedures physically remove bacterial colonies and plaque buildup from tooth surfaces and below the gum line.
The second part of treatment involves chemical management, primarily through systemic antibiotics. A common and effective antibiotic regimen for A.a. infections is a combination of amoxicillin and metronidazole. While mechanical cleaning is foundational, systemic antibiotics are often necessary to eliminate the pathogen from deep periodontal pockets.