Scanning electron microscopic examination of Bacteroides fragilis and Gardnerella vaginalis after exposure to concentration gradients of metronidazole and tinidazole.

Agar diffusion tests with metronidazole and tinidazole were performed with one strain each of Bacteroides fragilis and Gardnerella vaginalis (Haemophilus vaginalis, Corynebacterium vaginalis). Their cell morphology was studied 'in situ' on agar surfaces by means of scanning electron microscopy (SEM). A sharp growth end-point was found for B. fragilis, whereas with G. vaginalis there was a gradual decrease in the number and size of the colonies close to the agar well. The SEM study also revealed elongation of the B. fragilis cells when exposed to high concentrations of either drug. No such elongation of G. vaginalis was observed.