Identification of Actinobacillus actinomycetemcomitans: polymerase chain reaction amplification of lktA-specific sequences.

Actinobacillus actinomycetemcomitans has been strongly implicated in the etiology of localized juvenile periodontitis. Techniques used in the identification of this periodontal pathogen include cultural, biochemical, immunological and DNA hybridization analysis. In this study, we report the use of polymerase chain reaction (PCR) to amplify unique sequences of A. actinomycetemcomitans. Specific oligonucleotide primers LKT2 and LKT3 were designed to hybridize to the A. actinomycetemcomitans lktA gene, which encodes leukotoxin, a putative A. actinomycetemcomitans virulence factor. The LKT2 and LKT3 primers amplified lktA-specific sequences from all 12 A. actinomycetemcomitans strains tested. In another set of experiments, 13 other bacterial species, most of which are normal residents of the oral cavity, were tested with these primers. These PCR amplifications also contained 2 additional primers, RRN4 and RRN5, which served as positive controls; RRN4 and RRN5 were designed to amplify specific sequences of eubacterial 16S ribosomal DNA (rDNA). PCR amplifications of all bacterial species tested, including A. actinomycetemcomitans, yielded 16S rDNA-specific DNA fragments. Furthermore, each bacterial species tested, with the exception of A. actinomycetemcomitans, failed to amplify lktA sequences. The LKT and RRN primers were used in further PCR experiments to detect A. actinomycetemcomitans directly from gingival fluid samples. The results clearly demonstrate the simplicity, rapidity, specificity and accuracy of the LKT primers in the identification of A. actinomycetemcomitans.