Susceptibility of Bacteroides Species to Metronidazole during Treatment of Patients with Crohn's Disease and Healthy Individuals

Abstract

Patients with Crohn's disease are usually treated with metronidazole for long periods with the risk of selecting resistant bowel bacteria. This could have serious clinical and epidemiological implications, especially with regard to Bacteroides fragilis which is the most common cause of severe anaerobic infections. An investigation was therefore undertaken with the use of an agar dilution method to examine the susceptibility to metronidazole of B. fragilis and other common Bacteroides species isolated from faeces before, during and after treatment of patients with Crohn's disease and healthy individuals. Before treatment, or during medication with sulphasalazine, 88% of the strains tested showed minimum inhibitory concentrations (MIC values) of ≤1 mg/l and none had MIC values >4 mg/l. The MIC values were significantly increased during metronidazole treatment (p<0.02), with a maximum value of 8 mg/l. No significant changes were noted for the MIC values of strains isolated before and 1 week to 1 month after treatment (p>0.1). It is concluded that it is important to examine the MIC values of bacteroides isolates from patients with long term treatment with metronidazole, especially with regard to treatment failure.