Abstract
Susceptibility of Trichomonas vaginalis isolates to metronidazole was evaluated in vitro under aerobic and anaerobic culture conditions. Reliability of a commercial medium ÒFujiÓ for this purpose was confirmed by evaluating the growth and susceptibility to metronidazole of a reference strain of the protozoon, TS-1:KE10. Seventeen isolates of T. vaginalis were obtained from 5 hospitals in Tokyo, Kanagawa and Nagasaki. In contrast to 16 of the 17 isolates as well as TS-1 strain, virtually all of which had minimum lethal concentration (MLC) of metronidazole of less than 7.5 micro-g/ml under the anaerobic assay condition, one of the isolates KO-12 strain, survived at 7.5 micro-g/ml of metronidazole, the highest concentration tested in this study, and showed a significant growth from the 10th day of cultivation. This strain had been isolated from a patient with recurrent vaginal trichomoniasis treated in two courses of 500 mg oral metronidazole twice daily for 7 days with vaginal suppository of the same drug at 250 mg/day for 7 days. Under the aerobic assay condition, this strain showed MLC of 30 micro-g/ml, while that of KO-22 strain isolated from the same patient after the 2nd course of treatment was 60 micro-g/ml. Electron microscopic observation on KO-12 strain with or without 5 micro-g/ml metronidazole showed ultrastructural changes in hydrogenosome like aggregation of the organelle in the presence of metronidazole. These findings suggest that KO-12 strain is the first isolate of metronidazole-resistant T. vaginalis under the anaerobic condition in Japan. A definitive conclusion could not be drawn concerning the aerobic resistance of this protozoon because of the difference in the assay method employed.
Key words: Trichomonas vaginalis; Protozoa, parasitic; metronidazole; drug resistance.