Objective: This study characterized Actinobacillus actinomycetemcomitans isolates from young Chinese aggressive periodontitis patients.
Methods: Subgingival plaque samples (two/subject) were collected from diseased subjects < 25 years old (n = 9, mean age 21.1 +/- 1.6 years) and age-matched periodontitis-free controls (n = 47, mean age 22.0 +/- 1.1 years). Selective and anaerobic culture were used. The serotype, leukotoxin gene (ltx) operon promoter and the cytolethal distending toxin (cdt) genes complex of the A. actinomycetemcomitans isolates were investigated. Effects of the isolates on non-keratinizing periodontal ligament epithelial cells monolayer were studied.
Results: Diseased subjects had significantly higher full-mouth bleeding score (p = 0.002) and total viable counts from plaque samples (7.2 x 10(6) vs. 2.1 x 10(5) CFU/paperpoint, p < 0.005). A. actinomycetemcomitans was isolated from 67%/56% or 6%/4% of diseased or controls subject/sites, respectively (p < 0.001). The proportion of A. actinomycetemcomitans isolatable from aggressive periodontitis or periodontitis-free associated subgingival plaque was low (0.7% vs. 0.1%, p < 0.02). The serotype of the isolates was characterized. All isolates possessed 652-like ltx gene promoter and all but one serotype c isolate from a diseased patient had intact cdtABC genes. That particular strain appeared to confer the least cellular damages on periodontal ligament epithelial monolayer compared to others.
Conclusion: This preliminary study confirmed the notion of increased prevalence and quantity of A. actinomycetemcomitans associated with aggressive periodontitis in young patients. The overall ltx promoter and cdt characteristics of the A. actinomycetemcomitans isolates, however, were similar among the diseased and control groups. A strain lacking the cdtABC gene appeared to be less damaging to a periodontal ligament epithelial cell model. Further studies therefore are warranted to clarify the pathogenic role and potentials of A. actinomycetemcomitans in aggressive periodontitis.