Cytolethal distending toxin of Actinobacillus actinomycetemcomitans. Occurrence and association with periodontal disease.

The cytolethal distending toxin (Cdt) of Actinobacillus actinomycetemcomitans, a periodontal pathogen, is a newly described cytotoxin with immunosuppressive properties, capable of causing cell cycle arrest of lymphocytes. The objectives of this study were to investigate the occurrence of A. actinomycetemcomitans with the cdt genotype in the subgingival plaque of periodontitis patients and to determine the association of this bacterial genotype with periodontal disease. A total of 146 subgingival plaque samples from periodontitis patients were assayed by the PCR method using oligonucleotide primers targeting the cdt operon of A. actinomycetemcomitans. Primers targeting the leukotoxin gene A (ltxA) of A. actinomycetemcomitans was used to determine the occurrence of the bacteria in the plaque samples at baseline. At baseline, A. actinomycetemcomitans was detected in 106 out of 146 (73%) diseased sites studied. Among the 106 diseased sites found to harbor A. actinomycetemcomitans, 13 sites were positive for the bacteria with the cdt genotype (12%). Out of the 13 positive sites, 10 sites were obtained from patients diagnosed with aggressive periodontitis (77%). Thus, A. actinomycetemcomitans with the cdt genetic subtype has low occurrence in the subgingival plaque of periodontitis patients. However, a strong association was observed between the presence of the bacteria and aggressive forms of periodontitis. Thus, the cytotoxic and immunosuppressive properties of A. actinomycetemcomitans Cdt may function to cripple the host immunity and contribute to the pathogenesis of aggressive periodontitis.