Clonal infection with Actinobacillus actinomycetemcomitans following periodontal therapy

Mechanical debridement results in a shift of the bacterial composition in t he periodontal pocket on the species level. It is unknown, however, whether a clonal change within a species could lead to the emergence of strains wi th different levels of virulence. Therefore, in the present study, the gene tic variability of Actinobacillus actinomycetemcomitans was assessed and st rains identified which were associated with periodontal disease progression following periodontal therapy, i.e., refractory periodontitis. Twenty adul t patients with untreated periodontitis and subgingival colonization of A. actinomycetemcomitans were randomly assigned to receive full-mouth scaling alone or scaling with an adjunctive antimicrobial therapy. Both groups rece ived supportive periodontal therapy at 3, 6, 9, 12, 18, and 24 months. Subg ingival plaque samples were taken at every visit; venous blood was obtained at 24 months only. A. actinomycetemcomitans isolates were typed by the RAP D method, and antibody reactivity against outer membrane proteins was asses sed by immunoblot analysis. Eleven distinct RAPD patterns were found in 18 patients completing the study. All patients harbored only one A. actinomyce temcomitans genotype, and within each patient this genotype persisted throu ghout the 24-month observation period. No differences in the expression of antibody reactivity against outer membrane proteins were found between stra ins isolated at baseline and at 24 months. Three genotypes were associated with reduced survival rates of teeth without probing attachment loss of 2 m m or more. The results indicated that (i) most patients harbored only one A . actinomycetemcomitans genotype; (ii) the genotype persisted following the rapy; and (iii) only some genotypes were associated with refractory periodo ntitis.