Aerobic resistance ofTrichomonas vaginalisto metronidazole inducedin vitro

Abstract

SUMMARYAerobic resistance ofTrichomonas vaginalisto metronidazole was inducedin vitroby anaerobic cultivation of drug-susceptible trichomonads with low concentrations of the drug (2–3 μg/ml) for 50 days. Minimal lethal concentrations (MLC) for metronidazole of the resistant derivatives were high in aerobic susceptibility assays (MLC = 216–261.5 μg/ml) but low in anaerobic assays (MLC = 4.2–6.3 μg/ml), surpassing MLC values of their parent strain approximately 50-fold and 3-fold under aerobiosis and anaerobiosis, respectively. Sensitivity to metronidazole under anaerobic conditions and activity of the hydrogenosomal enzyme pyruvate: ferredoxin oxidoreductase indicated that the resistance was of the aerobic type. Dependence of the resistance manifestation on O2was further confirmed by susceptibility assaysin vitroperformed in defined gas mixtures of different oxygen content (1–20%). Five percent concentration of O2proved to be the threshold required for resistance demonstration and the MLC values further increased with increasing O2concentrations. Thein vitro-induced resistance was also demonstratedin vivoby subcutaneous mouse assay. The dose of metronidazole needed to cure 50% of infected mice (DC50) was 223 mg/kg × 3 for resistant derivative MR-3a but 6.6 mg/kg × 3 only for its drug-susceptible parent strain. The metronidazole – resistant strains developed in this study correspond by their properties to drug-resistantT. vaginalisstrains isolated from patients refractory to treatment, and promise to be a useful tool in the study of 5-nitroimidazole aerobic resistance.