Insights into life-cycle stage transition of Trichomonas vaginalis and advancement in its diagnosis

Abstract

Trichomonas vaginalis is a protozoan parasite and the causative agent of the most common non-viral, sexually transmitted disease (STD) in humans known as trichomoniasis. WHO estimates more than 270 million cases of trichomoniasis worldwide throughout the year. There is a lack in the understanding about its life cycle and mode of transmission. There are a few reports where non-sexual transmission is also observed, but the mechanism remains unclear. T. vaginalis is mostly prevalent in women in their reproductive age. Thus, the parasite must deal with changes in vaginal epithelium, cervical mucus, pH, redox potential, and overall modulation of the vaginal microbiome that occurs during the menstrual cycle. The survival and success of the parasite requires a robust and specialized machinery to tackle these stresses. The only drug of choice for trichomoniasis is metronidazole and drug-resistance are on the rise. There is also a lack of accurate diagnosis for the detection of T. vaginalis infection as the current diagnosis is mostly based on the clinical presentation of symptoms and is inaccurate. The life cycle of Trichomonas vaginalis possess a trophozoite form which is transmitted sexually. In our study, we demonstrated the presence of Cyst-like structures (CLS) in the life cycle of T. vaginalis and characterized it under different stress conditions. This CLS form can survive in unfavourable conditions such as osmotic imbalance and presence of detergents and possess a thick cell membrane. This CLS stage can convert back to trophozoite form when favourable conditions return. The CLS form was observed to co-exist with trophozoite form in vivo in patient’s vaginal swab samples, indicating that CLS can also be infective. To understand the mechanism of formation of CLS, we have performed 2DGE and mass spectrometry based in-depth proteomics by using label free approach. We observed that the morphological transformation from trophozoite to CLS is coupled to less metabolic activity and alterations in proteins of adhesion and cytoskeletal reorganization. We also observed metronidazole resistance in CLS which is in range of the drug resistance observed in trophozoite forms of resistant strains. In addition, we have biochemically characterized an important organelle present in Trichomonas known as hydrogenosome. Using mass spectrometry, we performed an exhaustive proteomics analysis to classify the identified proteins into their functional pathways. The study allows understanding of this ill-explored organelle present in an early branching eukaryote. We have developed a point-of-care diagnostic test for the detection of antibodies against the T. vaginalis infection in humans, which can be used in healthcare settings for accurate diagnosis. Altogether, our study establishes a transmissible stage in the life cycle of T. vaginalis which can be transmitted non-sexually. In addition, the study highlights metabolic characterization, emergence of drug resistance and development of its point-of-care diagnostic tool for its infection.