Actinobacteria are normally present in the gums and are the most common cause of infection in dental procedures and oral abscesses. Many "Actinomyces" species are opportunistic pathogens of humans and other mammals, particularly in the oral cavity. In rare cases, these bacteria can cause actinomycosis, a disease characterized by the formation of abscesses in the mouth, lungs, or the gastrointestinal tract. Actinomycosis is most frequently caused by "A. israelii", which may also cause endocarditis, though the resulting symptoms may be similar to those resulting from infections by other bacterial species. "Aggregatibacter actinomycetemcomitans" has been identified as being of note in periodontal disease.