Antibiotic resistance of an endodotitis-associated bacterium, Porphyromonas endodontalis.

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Porphyromonas endodontalis, a Gram-negative, black-pigmented, anaerobic rod, is considered to be associated with endodontitis. A nonpigmentd variant, KSEW01, from KSE105 which is a clinical isolate from an endodontic lesion and is possibly a parent strain of KSEW01, was found to be resistant against a glycopeptide antibiotic reagent, or a dalbaheptide, vancomycin (VCM), of which the minimal inhibitory concentration (MIC) was greater than 200 mug/ml. To help understand the mechanism of the antibiotic resistance in anaerobes, the cellular proteins of KSEW01 which was cultured in the presence of and those in the absence of vancomycin were compared by the two dimensonal polyacrylamide gel electrophoresis to detect the component(s) that might give the antibiotic resistance to this strain. A clear spot which was present in the cell cultured with VCM and absent without VCM was found. Regretfully the result was not reproducible. Then, thirty-four VCM-resistant mutants from KSE105, five from P.endodontalis type strain, ATCC35406, were obtained in vitro. MICs of these mutants were measured by agar dilution method. The mutants obtained were all black-pigmented. Some of the mutants had the resistance against VCM to the same degree (MIC, 200 mug/ml) as that of KSEW01. All the three black-pigmented, spontaneous revertants of KSEW01 were isolated and they were also resistant against VCM (MIC, 100 mug/ml). From these results, pigmentation and VCM resistance were not linked together. The detection of the difference between the cellar components of KSE105 and those of the VCM-resistant mutants are under investigation. The results will be applied to a potent pathogen of adult periodontitis, Porphyromonas gingivalis.