Isolation and identification of bacteria from subgingival plaque with low susceptibility to minocycline

Twenty subgingival plaque samples from patients with chronic periodontitis were screened for the presence of three periodontal 'pathogens'--Porphyromonas gingivalis, Fusobacterium nucleatum and Eikenella corrodens. Nineteen of the samples were found to contain at least one of the three organisms and six samples contained all three. The subgingival plaque samples were cultured in the presence of various concentrations of minocycline, and those organisms which appeared to be least susceptible to the antibiotic were isolated and identified. A total of 40 isolates were obtained and these consisted of 18 different species, only one of which, Fusobacterium nucleatum, is generally recognized as being associated with chronic periodontitis. The minimum inhibitory concentrations of minocycline for many of the organisms isolated were greater than the concentration of attainable in gingival crevicular fluid following routine parenteral administration of the antibiotic.