Exploring drug resistance and genetic polymorphisms in Iranian Trichomonas vaginalis isolates: focused on the ntr4Tv and ntr6Tv genes

Urogenital trichomoniasis, caused by Trichomonas vaginalis, is primarily treated with nitroimidazoles. However, rising treatment failures and resistance have become a public health concern. The aim of the study was to evaluate the metronidazole susceptibility pattern of Iranian T. vaginalis isolates. This study analyzed 36 isolates, comprising 9 fresh clinical isolates obtained from consenting women attending gynecological clinics in Quds city, Tehran province, and 27 archival isolates from Hamadan province. Genetic characterization of the two nitroreductase genes, ntr4_Tv and ntr6_Tv, associated with metronidazole resistance, was performed in all isolates. Additionally, the archival isolates underwent in vitro drug susceptibility testing. The prevalence of trichomoniasis among women was 0.59% (95% CI: 0.51–0.67; 9/1525). Sequence analysis identified eight point mutations in ntr4_Tv and ten in ntr6_Tv, producing nine and six haplotypes, respectively. No genetic mutations associated with metronidazole resistance were identified in the analyzed isolates. Drug susceptibility testing indicated that the isolates were susceptible to metronidazole. Under aerobic conditions, 48-hour minimum lethal concentrations ranged from 1.6 to 25 μg/mL, with a mean of 9.6 ± 6.8 μg/mL. The prevalence of trichomoniasis in this region is significantly lower than global estimates, suggesting that alternative etiological agents should be prioritized in the differential diagnosis of vaginitis. Despite demonstrated metronidazole susceptibility among current isolates, robust surveillance integrating phenotypic drug testing and molecular resistance profiling is critical for sustained treatment efficacy and antimicrobial stewardship.