Trichomonas vaginalis (Tv) is a protozoan that causes the most common sexually transmitted infection worldwide. It has been associated with increased risk of HIV infection, cervical cancer and preterm delivery. Current treatment consists of oral 5-nitroimidazoles (5-NI) metronidazole (Mz) and tinidazole (Tz), but refractory cases are on the rise. Tv lacks mitochondrion and relies on the hydrogenosome for ATP production and 5-NI activation. Drug resistance mechanisms involve oxygen competing with 5-NI for electrons and inactivation of hydrogenosomal reductases.
Antimicrobial assays were done as survival assays with a 24 h growth and ATP content as the read-out. EC50s were used to generate a distance matrix table and create tree diagrams; clustered branches were determined as “resistance groups”. Expression levels of 17 key genes were assessed by real-time PCR.
From anaerobic screening, 63 compounds were found to be more potent than Mz/Tz. Clustering of their activities revealed five distinct resistance groups. Oxygen caused increase in drug resistance in all strains. Real-time PCR revealed down-regulation of FR3, FR6, FR7, PFOR E and ME in one resistance group compared with the others.
This study shows the potency of new 5-NI derivatives, the role of oxygen in increasing resistance, and the down-regulation of several enzymes involved in drug activation in one resistance group. These findings suggest that different resistance mechanisms exist and provide new tools to functionally stratify drug resistance phenotypes in Tv, thus informing the development of new 5-NI compounds against Mz-resistant Tv strains.
L. Eckmann, None