Campylobacter rectus, a gram-negative, microaerophilic, and motile bacterium, has been proposed to play a pathogenic role in human periodontitis. Surface components, such as the flagellum, surface layer (S-layer), and cytotoxin, have been reported as possible virulence factors of the microorganism. In the present study, monoclonal antibodies against surface components of this bacterium were produced to detect and investigate the pathogenic potential of C. rectus in periodontitis. Two monoclonal antibodies, designated CRT-1 and CRT-2, recognized a peculiar 150 kDa S-layer protein by immunoblot analysis. The CRT-2 antibody reacted to all C. rectus strains tested, except for the S-layer negative strain of the species [C. rectus ATCC 33238 S-layer (-) strain]. The CRT-3 antibody reacted to a 60-kDa protein in C. rectus and also cross-reacted with Campylobacter showae ATCC 51164 and CCUG 11641 strains. Using the dot-blot method, we were able to detect C. rectus using the CRT-2 antibody when as few as 103 organisms were present in a subgingival dental plaque sample. Detection of C. rectus in plaque samples correlated significantly with clinical findings such as probing depth (P < 0.001), bleeding on probing (P < 0.001), and gingival index (P < 0.001). These findings indicate that infection by C. rectus may be an important indicator of periodontal disease status.
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