A Tissue Culture Model for Study of Growth Promotion and Antimicrobial Susceptibility in Bacteroides Fragilis

A new model for testing the susceptibility of anaerobic bacteria under in-vivo oxygen pressure is described. Bacteroides fragilis was incubated with a monolayer of mouse fibroblasts or with Escherichia coli or with both in tissue culture medium exposed to an aerobic atmosphere with 5% CO2. B. fragilis started to multiply when the oxygen pressure of the medium was approximately 13 kPa. The resulting growth curves were similar whichever promoter was used. However, the reduction of the medium took place much earlier in the presence of E. coli. This may explain the excellent effect of metronidazole on B. fragilis in the E. coli combinations and its solely bacteriostatic effect in the plain tissue culture. Imipenem exerted a bactericidal effect in all systems and was the most potent agent tested.