Susceptibility of small-sized oral spirochetes to eight antibiotics and chlorhexidine.

The purpose of the study was to examine the susceptibility of two different small-sized spirochete morphotypes from subgingival plaque to eight antibiotics and chlorhexidine. MIC-values were determined by a broth dilution method and related to achievable antibiotic tissue- and blood concentrations. The spirochetes were characterized as susceptible, moderate susceptible, and resistant to the different antibiotics. The MICs of tetracycline hydrochloride, doxycycline, penicillin G, and chlorhexidine were all considerably lower for spirochete strains with a 2:4:2 endoflagella system (two endoflagella from each cell-end) than for strains with a 1:2:1 endoflagella system (one endoflagellum from each cell-end). No differences were observed for the remaining antibiotics. Spirochetes containing one endoflagellum from each cell-end were found to be susceptible to metronidazole and doxycycline, susceptible to moderate susceptible to tetracycline hydrochloride, moderate susceptible to penicillin G, and resistant to the remaining antibiotics. Spirochetes containing two endoflagella from each cell-end were susceptible to doxycycline, tetracycline hydrochloride, and metronidazole. Susceptible to moderate susceptible to penicillin G. These spirochetes were resistant to the remaining agents. The significance of these observations is discussed in relation to obtainable gingival crevicular fluid concentrations and treatment of marginal periodontitis.