Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans) is a Gram-negative, facultative nonmotile, rod-shaped oral commensal often found in association with localized aggressive periodontitis, a severe infection of the periodontium, although it is also associated with nonoral infections. Its role in periodontitis was first discovered by Danish-born periodontist Jørgen Slots, a professor of dentistry and microbiology at the University of Southern California School of Dentistry.