[Susceptibility of potential periodontopathic bacteria to metronidazole, spiramycin and their combination].

A total of 65 bacterial strains originating mostly from subgingival plaque were tested for their susceptibilities to metronidazole, spiramycin, and their combination, ornidazole, erythromycin and tetracycline by means of an agar dilution technique. All agents were active against all anaerobic Gram-negative rods. Bacteroides gingivalis and Fusobacterium nucleatum showed marked susceptibility to metronidazole (MIC less than or equal to 0.06 microgram/ml) whereas 4-64 micrograms/ml were required to inhibit the capnophilic Actinobacillus actinomycetemcomitans and Capnocytophaga. Gram-positive facultatives were resistant to nitro-imidazoles but were inhibited at macrolide concentrations less than or equal to 0.5 microgram/ml. Except for F. nucleatum and Veillonella strains (2 less than or equal to MIC less than or equal to 128 micrograms/ml) macrolides were active against all other anaerobic bacteria tested. At concentrations less than or equal to 2 micrograms/ml the combination of spiramycin and metronidazole (2 : 1) was active against virtually all bacteria tested but our results failed to show a synergistic effect.