Clinical and molecular correlates of metronidazole resistance in Trichomonas vaginalis: a cross-sectional study from a tertiary-care centre in western India

Trichomoniasis, caused by the flagellated protozoan Trichomonas vaginalis , is the most prevalent non-viral sexually transmitted infection worldwide. Treatment relies mainly on metronidazole, although resistance increasingly contributes to treatment failure. The nitroreductase genes ntr4 and ntr6 have been implicated in metronidazole resistance, but data from Indian clinical settings remain limited. This hospital-based cross-sectional study was conducted at AIIMS Rajkot between March 2024 and February 2026 among symptomatic women aged 18–55 years. Vaginal aspirates were processed by wet-mount microscopy and cultured in modified cysteine–peptone–liver–maltose medium under microaerophilic conditions. All culture-confirmed isolates underwent broth microdilution minimum inhibitory concentration testing for metronidazole and PCR screening for ntr4 and ntr6 genes. Of 210 women enrolled, Trichomonas vaginalis was isolated from 28 (13.3%; 95% CI 9.1–18.6%). Four isolates (14.3%; 95% CI 4.0–32.7%) demonstrated phenotypic metronidazole resistance (MIC ≥ 8 µg/mL), while 24 were susceptible (MIC ≤ 1 µg/mL). All four resistant isolates were recovered from women with documented metronidazole exposure within the preceding six months, compared with 8 of 24 (33.3%) women whose isolates were susceptible (Fisher’s exact test, P = 0.024). Conventional PCR yielded a discrete ntr4 amplicon (549 bp) in all four resistant isolates and in none of the 24 susceptible isolates or negative control; ntr6 amplification was not detected in any isolate. The significant association between phenotypic resistance and ntr4 detection supports a nitroreductase-mediated resistance mechanism in recurrent or treatment-refractory trichomoniasis.