Objectives: The occurrence of the protease genes rgpA and rgpB in clinical isolates of the periodontal pathogen Porphyromonas gingivalis was investigated in order to evaluate the potential feasibility of using rgpA and rgpB genes as markers to identify P. gingivalis in clinical specimens. Methods: DNA was extracted from 13 P. gingivalis clinical isolates, from 13 periodontitis patients, presumptively identified via phenotypic characteristics and species-specific whole genomic DNA probes, and used as template in polymerase chain reaction (PCR) assays with 16 S rRNA-based primers specific to P. gingivalis, as well as rgpA and rgpB specific primers designed to amplify the catalytic domains of gingipain-R1 and gingipain-R2, respectively. Dilutions of DNA from P. gingivalis FDC 381 were used to test the sensitivity of the assays, and strains of Actinobacillus actinomycetemcomitans, Bacteroides forsythus, Campylobacter rectus, and Prevotella intermedia were used to evaluate assay specificity. Boiled bacterial pellets from 20 additional P. gingivalis clinical isolates were also used as templates in PCR testing with the gingipain-R1 specific primers. Results: Species-specific 16S rRNA primers confirmed P. gingivalis identification for 10 of the 13 presumptively-identified clinical isolates. The rgpA genes primers were found to be specific to P. gingivalis at a threshold of 3.1 pg DNA, and identified the rgpA gene in 7 of the 10 clinical P. gingivalis isolates. In contrast, the rgpB gene was found in only 2 of 10 clinical P. gingivalis isolates. While boiled pellets from 17 of 20 P. gingivalis clinical isolates tested positive in at least one assay, poor test reproducibility was found. Conclusions: The rgpA protease gene occurred more frequently in clinical P. gingivalis isolates than the rgpB genotype, indicating genetic diversity among P. gingivalis strains recovered from human periodontitis patients. Boiled pellets of P. gingivalis cells appear to be poor template sources for PCR assays.

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