IDENTIFICATION AND CHARACTERIZATION OF GENETIC CLUSTER GROUPS OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS ISOLATED FROM THE HUMAN ORAL CAVITY

Actinobacillus actinomycetemcomitans is recognized as a primary pathog en in localized juvenile periodontitis (LJP). Restriction fragment len gth polymorphisms (RFLP) within a collection of subgingival plaque iso lates of this bacterium were identified and characterized as the first step in understanding the pathogenesis of LJP. Over 800 isolates, fro m members of 18 families (LJP families) with at least one member with active LJP or a documented history of the disease and one or more sibl ings, less than 13 years of age, having no clinical evidence of LJP an d 32 healthy control subjects, were assigned to one of 13 distinct RFL P groups (II to XIV) by using a previously characterized 4.7-kb DNA pr obe cloned from the reference strain FDC Y4. Isolated belonging to RFL P groups II, IV, V, and XIII predominated subgingival sites in the sub jects. Members of RFLP groups II, IV, VII, VIII, X, and XI were recove red only from LJP family subjects, while group XIII and XIV variants w ere found exclusively in healthy controls. A synthetic oligonucleotide , homologous to the 5' end of the leukotoxin gene (lktA), and the A. a ctinomycetemcomitans plasmid, pVT745, were tested for their abilities to subdivide the 13 RFLP groups. The leukotoxin probe specifically ide ntified all RFLP group II variants because of the absence of a HindIII site in the upstream noncoding region of the lkt gene complex. The pl asmid probe was not as selective but may be useful for identifying cli nical isolates belonging to RFLP group I. The use of these probes for the identification of genetic variants of A. actinomycetemcomitans tha t may preferentially colonize diseased and healthy subjects will facil itate the study of the role of this important pathogen in periodontal diseases.