Abstract
Aggregatibacter actinomycetemcomitans is a periodontal pathogen colonizing the oral cavity in many individuals of the human population. It is equipped with several potent virulence factors that can cause cell death and induce or evade the host inflammatory response. Both harmless and highly virulent genotypes of the bacterium have emerged because of the large genetic diversity within the species. The oral condition and age, as well as the geographic origin of the individual, influence the risk to be colonized by a virulent genotype of the bacterium. In the present editorial, the different genetic and virulence properties of A. actinomycetemcomitans will be addressed in relation to the publications in this Special Issue.