Rapid Identification of Periodontal Pathogens in Subgingival Dental Plaque: Comparison of Indirect Immunofluorescence Microscopy with Bacterial Culture for Detection of Bacteroides gingivalis

Abstract

A large body of research implicates Bacteroides gingivalis in the etiology of adult periodontitis, however, the application of this information to clinical diagnosis and treatment has been hampered by the need for a simple, rapid, and reliable means of detecting this microorganism. In the present study, indirect immunofluorescence microscopy using species specific, polyclonal antisera and a monoclonal antibody was evaluated in the clinical identification and quantitation of B. gingivalis in human subgingival dental plaque. One hundred and twenty subgingival plaque samples were obtained from predetermined sites by means of sterile paper points from 20 human subjects including 10 adult periodontitis patients and 10 periodontally normal subjects. The proportions of cultivable B. gingivalis in each sample were determined following anaerobic culture on nonselective blood agar media and selective media containing kanamycin. These results were then compared to quantitative estimates of B. gingivalis by indirect immunofluorescent microscopic evaluation of heat-fixed plaque smears. Using both immunofluorescence microscopy and bacterial culture, the present study confirms the importance of B. gingivalis in adult periodontitis previously described by culture. The organism was cultivable from 70% of the adult periodontitis patients but not from any of the normal adults. In contrast, indirect immunofluorescence microscopy detected the organism in up to 40% of the subgingival sites in 100% of the adult periodontitis patients as well as four sites in the periodontally normal subjects. The sensitivity of indirect immunofluorescence microscopy compared to culture ranged from 91 to 100% while the specificity varied from 87 to 89%. The numbers of B. gingivalis identified by immunofluorescence microscopy were directly proportional to the severity of periodontal disease as measured by clinical indices. Linear regression analysis of the immunofluorescent data suggests that the probability of a subject having adult periodontitis approaches 100% when B. gingivalis comprises 9% or more of the subgingival microflora. The present study indicates that indirect immunofluorescence microscopy using speciesspecific serodiagnostic reagents is useful in the clinical detection of B. gingivalis in human subgingival dental plaque. The data also suggests that certain cases of adult periodontitis can be diagnosed solely on the basis of this laboratory test.