Aggregatibacter actinomycetemcomitans is an oral commensal found also in severe infections in the oral cavity, mainly the periodontium. A. actinomycetemcomitans, previously Actinobacillus actinomycetemcomitans, is a gram negative facultative non motile rod. It is also associated with non oral infections. Recent studies have shown a phylogenetic similarity of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus, Haemophilus paraphrophilus, and Haemophilus segnis suggesting the new genus Aggregatibacter for them. It is one of the bacteria which might be implicated in destructive periodontal disease. Although it has been found more frequently in localized aggressive periodontitis, prevalence in any population is rather high. It has also been isolated from actinomycotic lesions (mixed infection with certain Actinomyces species, in particular Actinomyces israelii). It possesses certain virulence factors that enable it to invade tissues, such as leukotoxin.
