Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 11 1 2016 03 14 46 51 Mohammad MATINI Dept. of Medical Parasitology and Mycology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran AND Dept. of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Amir-Hossein MAGHSOOD Dept. of Medical Parasitology and Mycology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran Mahdi MOHEBALI Dept. of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran Soghra RABIEE Dept. of Obstetrics and Gynecology, Fatemieh Women Hospital, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran Mohammad FALLAH Dept. of Medical Parasitology and Mycology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran Sassan REZAIE Dept. of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mostafa REZAEIAN Dept. of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran 2016 03 14 2016 03 14 Background: Metronidazole, a 5-nitroimidazole derivative, is the main antitrich­omonal agent of choice for treatment of trichomoniasis. Since 1962, some cases of treatment failure with metronidazole have been reported and recently drug re­sistance is now on the rise in the world. This study was aimed to determine current susceptibility of Iranian isolates of Trichomonas vaginalis to metronidazole. Methods: This study was performed on 50 T. vaginalis isolates collected from west and central areas of Iran. After axenisation of the parasites, susceptibility testing was carried out by using serial twofold dilutions of metronidazole (400 to 0.1 µg/ml). The minimum inhibitory concentration (MIC) and the minimum lethal concentration (MLC) of the trichomonads were determined after 48 h incubation at 35.5 °C. Drug susceptibility assays of the all isolates were carried out two times in triplicate under aerobic and anaerobic conditions. Results: Ninety-eight percent of the T. vaginalis isolates (49/50) were sensitive to metronidazole. Metronidazole resistance was defined as aerobic MIC ≥50 µg/ml, detected in one isolate. The means of aerobic MICs and MLCs and that of anaero­bic MICs of the parasites were 2.91, 1.95 and 0.28 µg/ml, respectively. Conclusion: This investigation showed in vitro low-level tolerance to metronida­zole in a few T. vaginalis isolates that may be leading to the development of drug resistance. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/809 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/809/652