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Bacteroides forsythus has been associated with destructive adult periodontitis. Up to now, detailed analysis by classical means was hampered by the fastidious nature of the organism. There is hope that the application of molecular detection methods such as indirect immunofluorescence or in situ hybridization (ISH) will allow for more rapid and accurate identification. Here we describe a B. forsythus-specific probe (BFV530), complementary to 16S rRNA, which correctly identified all B. forsythus isolates as confirmed by biochemical, protein, or fatty acid analysis. To assess whether this probe might be suitable for direct identification of B. forsythus in clinical specimens, a total of 92 subgingival plaque samples were analyzed. Fifty-five specimens were tested in parallel by culture, light microscopy, and filter hybridization. Unfortunately, the overall agreement between results of filter hybridization and conventional methods was 70.9% only. We therefore examined 37 new specimens by ISH and indirect immunofluorescence by using fluorescently labeled probe BFV530 or B. forsythus-specific monoclonal antibody 116BF1.2 (kindly provided by R. Gmür, Zurich, Switzerland), respectively. Agreement between these methods was 100%, indicating that ISH with probe BFV530 might be used to accurately identify B. forsythus directly in subgingival plaque samples.

Fluorescent oligonucleotide probes complementary to variable regions of Porphyromonas gingivalis and Bacteroides forsythus 16S ribosomal RNA were used to identify these organisms in smears of formaldehyde-fixed subgingival plaque samples from patients suffering from periodontitis. Fluorescence in situ hybridization represents a useful method for assessing the microbial ecology of the periodontal flora.