RACIAL TROPISM OF A HIGHLY TOXIC CLONE OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS ASSOCIATED WITH JUVENILE PERIODONTITIS

Actinobacillus actinomycetemcomitans strains,vith enhanced levels of p roduction of leukotoxin are characterized by a 530-bp deletion from th e promoter region of the leukotoxin gene operon. Previous isolates wit h this deletion constituted a single clone belonging to serotype b, al though they displayed minor differences among each other. We have anal yzed the geographic dissemination of this clone by examining 326 A. ac tinomycetemcomitans isolates from healthy and periodontally diseased i ndividuals as well as from patients with different types of extraoral infections originating from countries worldwide. A total of 38 isolate s, all belonging to the same clone, showed the 530-bp deletion. Compar ison of a 440-bp sequence from the promoter region of the leukotoxin g ene operon from 10 of these strains revealed complete identity, which indicates that the deletion originates from a single mutational event. This particular clone was exclusively associated with localized juven ile periodontitis (LJP). In at least 12 of 28 families from which the clone was isolated, more than one family member had LJP. Notably, all the subjects carrying this clone had a genetic affiliation with the Af rican population. These observations suggest that juvenile periodontit is in some adolescents with an African origin is associated with a dis seminating clone of A. actinomycetemcomitans.