Investigation of In Vitro Metronidazole Resistance in the Clinical Isolates of Trichomonas vaginalis

Trichomonas vaginalis, a flagellated, urogenital anaerobic protozoon is reported as an important cause of vaginitis with a global distribution. Although metronidazole is the primary choice of drug for the treatment of trichomoniasis, the presence of resistant isolates from many different countries highlights the need of novel drugs for the treatment. Many studies from Turkey mostly dealing with the in vitro effects of compounds and natural products against T. vaginalis have been reported, however, only one study has been encountered searching the metronidazole resistance in a single T. vaginalis isolate. The aim of this study was to determine the in vitro metronidazole resistance and minimum lethal concentrations (MLCs) of the isolates from symptomatic cases. T. vaginalis strains isolated from vaginal discharge samples of symptomatic women that were sent to Adnan Menderes University Faculty of Medicine, Research and Training Hospital Parasitology Laboratory, between 2009-2014 period, were included in the study. The strains were isolated by the inoculation of samples into trypticase-yeast-maltose medium supplemented with 10% fetal calf serum. A total of 40 T. vaginalis isolates stored by cryopreservation were revived before the experiments. T. vaginalis trophozoites were incubated with different concentrations of metronidazole (200, 100, 50, 25, 12.5, 6.25, 3.12, 1.56 mu g/ml) and the viability of cells were examined in both aerobic and anaerobic conditions under phase contrast microscope. Additionally, non-motile isolates were further inoculated into fresh media and viability was checked. The wells containing motile trophozoites after 48 hours of incubation with 15 mu g/ml and/or higher metronidazole concentration in anaerobic condition and 75 mu g/ml and/or higher metronidazole concentration in aerobic conditions were determined as resistant isolates. Of the 40 T. vaginalis isolates three (7.5%) were resistant to metronidazole. MLC mean values of metronidazole-sensitive isolates were 27.17 mu g/ml in aerobic and 7.75 mu g/ml in anaerobic conditions. The rate of metronidazole resistance detected in this study was higher than most of reports from different countries. Despite being limited to the isolates from Aydin province (located at Agean region of Turkey), the present study has a value as it presented the existence of metronidazole-resistant isolates in Turkey for the first time. More research from other parts of Turkey is needed to better understand the metronidazole resistance at a national scale and to investigate novel strategies for the treatment. Moreover, further studies need to be carried out in order to clarify the relationship between clinical treatment response and in vitro metronidazole resistance in trichomoniasis.