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Abstract
Actinobacillus actinomycetemcomitans is a gram-negative pathogen that causes human severe periodontitis. The most intensively studied virulence factor of this bacterium is a pore-forming cytotoxin termed leukotoxin. Production of leukotoxin varies considerably among A. actinomycetemcomitans strains. Interstrain variations in leukotoxin production are thought to derive from differences in structure of the leukotoxin promoter region. In addition, several studies showed that culture conditions are also important factors influencing leukotoxin production levels. Export of A. actinomycetemcomitans leukotoxin across the cell envelope is likely mediated by a type I secretion system. Furthermore, it has also been suggested that outer membrane vesicles are involved in extracellular localization of the leukotoxin. This review summarizes current knowledge on the genetic and environmental factors affecting leukotoxin production and the export pathway for extracellular localization of leukotoxin.