Metronidazole susceptibility testing of anaerobic bacteria associated with periodontal disease

The aim of the present investigation was to determine the susceptibility of Prevotella intermedia, Porphyromonas gingivalis, Fusobacterium and Peptostreptococcus micros to metronidazole in vitro. Two methods were applied on each isolated strain: agar dilution and epsilometer Etest. A total of fifty three wild test strains (13 P.intermedia, 14 P. gingivalis, 14 F.spp and 12 P.micros) were isolated from patients with periodontitis. The Etest appears to be a simple, rapid and reliable method for the metronidazole susceptibility testing. The results show that all P.intermedia, P.gingivalis and F.spp strains were susceptible to metronidazole. The mean values of minimal inhibitory concentration obtained with the agar dilution method were, respectively, 0.98 microg/ml, 0.122 microg/ml and 0.242 microg/ml. For P.micros, the minimal inhibitory concentration was of 12.14 microg/ml. Comparatively to break points, only 60% of P.micros strains seem to be susceptible, in vitro, to metronidazole. This study demonstrated the excellent activity of metronidazole against P.intermedia, P.gingivalis, F.spp except perhaps for P.micros.