Strain of Trichomonas vaginalis resistant to metronidazole and other 5-nitroimidazoles.

A strain of Trichomonas vaginalis (IR-78), recently isolated from a patient afflicted with recurrent symptomatic trichomoniasis, showed resistance to metronidazole, tinidazole, and nimorazole in vitro as well as in vivo. In a serial dilution test using cysteine monohydrochloride-peptone-liver infusion-maltose medium, T. vaginalis IR-78 was only resistant under aerobic conditions. Under anaerobic conditions it was as susceptible as the normal reference strain. The minimal lethal concentrations of metronidazole, tinidazole, and nimorazole for IR-78 were 100, 50, and 50 mug/ml aerobically and 0.4, 0.4, and 0.2 mug/ml anaérobically, respectively. The efficacy of metronidazole, tinidazole, and nimorazole was assessed in vivo by oral administration to mice simultaneously infected with IR-78 both subcutaneously and intraperitoneally. The CD(50) (dose needed to cure 50% of infections) of each compound was significantly higher for the subcutaneous than for the intraperitoneal infection. In contrast, there was little difference in CD(50) for these infections in mice inoculated with a susceptible trichomonas strain. The CD(50)'s for all three compounds against intraperitoneal and subcutaneous infections with IR-78 were 2 to >70 times higher than for susceptible strain E. Both forms of infection with IR-78 could always be cured with therapeutically acceptable doses of tinidazole and nimorazole; subcutaneous infections could not be cured with tolerated doses of metronidazole.