Clonal diversity of Actinobacillus actinomycetemcomitans isolates from young adults with minimal periodontal disease

Actinobacillus actinomycetemcomitans is a major periodontal pathogen which is associated with both early-onset periodontitis and adult cases refractor y to conventional periodontal therapy, although the organism has also been shown to be widely distributed among dentate healthy individuals. The obser ved disease status may be associated with a variation in virulence of diffe rent strains or clones. The aim of the present study was to analyse genotyp e distribution as assessed by an arbitrarily primed polymerase chain reacti on (AP-PCR) among 51 isolates of A. actinomycetemcomitans recovered from mo re than 200 young adult recruits with no or minor periodontal disease. In a ddition, isolates from 25 periodontitis patients as well as reference strai ns were genotyped. Primers amplifying (i) a specific sequence in the ltxA r egion, (ii) a specific 16S rRNA sequence and (iii) sequences in the leukoto xin promoter region were used to verify species identity of the strains. Th ree random oligonucleotide primers were employed to analyse genomic polymor phisms of the organism by means of PGR. A total of 19 genotypes could be di stinguished, which were grouped by cluster analysis into 5 major clusters b ased on genetic similarity and a complete linkage sort. Whereas 3 clusters assembled A. actinomycetemcomitans genotypes isolated from both healthy sub jects and periodontitis patients, one cluster containing 4 different genoty pes exclusively comprised isolates from healthy or gingivitis subjects. Ano ther cluster with 2 genotypes consisted of strains originating from periodo ntitis patients (p < 0.05). One strain characterized by a specific 530 bp d eletion in the promoter region of the leukotoxin region was identified in a Ghanese patient with localized juvenile periodontitis. It was concluded th at there is considerable clonal diversity of A. actinomycetemcomitans strai ns isolated from healthy or periodontally diseased subjects, and that genet ically closely related groups might be associated with health or disease.