Virulence Factors of the Periodontopathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is an important periodontopathogen that has been implicated in juvenile and adult periodontitis. This capnophilic coccobacillus elaborates a number of virulence factors such as a bacteriocin, chemotaxis-inhibiting factor, immunosuppressive factors, cytotoxic factors, Fc binding proteins, lipopolysaccharide (LPS), collagenases, antibiotic resistant determinants, adhesins, and invasins. The adhesins are associated with the bacterial surface or released into the surrounding environment in the form of vesicles. Adhesion to epithelial cells involves multiple determinants and is influenced by both bacterial and host environmental conditions. Invasion is a rapid process which occurs within 15 minutes post-infection. Host cell actin is polymerized around the invading bacteria. Bacteria enter through a membraneruffled region of the host cell. This internalization process triggers vesicle formation on the bacteria. A. actinomycetemcomitans is taken up in a vacuole but is seen free in the cytoplasm in a short period of time. The number of internal organisms does not increase with time. A. actinomycetemcomitans can transcytose through the epithelial cells and is released from the host cell in 5 hours. We hypothesize that A. actinomycetemcomitans uses invasion of the epithelial cell as a mechanism to penetrate deeper tissues by cell-to-cell spread. J Periodontol 1996;67:291-297.