Oxygen-dependent metronidazole-resistance of Clostridium histolyticum.

Sensitivity determinations with 6 strains of Clostridium histolyticum showed that the inhibitory action of metronidazole was highly dependent on the oxygen concentration of the environment. Under anaerobic conditions they were sensitive but at increased oxygen concentrations moderately sensitive or resistant. The flexible resistance of this aerotolerant anaerobe against metronidazole may interfere with results of sensitivity determinations, estimation of blood levels and it may influence the effectiveness of the drug in anaerobic infections due to aerotolerant anaerobes.