Metronidazole resistance of Trichomonas vaginalis as a cause of treatment failure in trichomoniasis--A case report

The retromer and retriever systems are conserved and differentially expanded in parabasalids

Early endosomes sort transmembrane cargo either for lysosomal degradation or retrieval to the plasma membrane or the Golgi complex. Endosomal retrieval in eukaryotes is governed by the anciently homologous retromer or retriever complexes. Each comprises a core tri-protein subcomplex, membrane-deformation proteins and interacting partner complexes, together retrieving a variety of known cargo proteins. Trichomonas vaginalis, a sexually transmitted human parasite, uses the endomembrane system for pathogenesis. It has massively and selectively expanded its endomembrane protein complement, the evolutionary path of which has been largely unexplored. Our molecular evolutionary study of retromer, retriever and associated machinery in parabasalids and its free-living sister lineage of Anaeramoeba demonstrates specific expansion of the retromer machinery, contrasting with the retriever components. We also observed partial loss of the Commander complex and sorting nexins in Parabasalia but complete retention in Anaeramoeba. Notably, we identified putative parabasalid sorting nexin analogs. Finally, we report the first retriever protein localization in a non-metazoan group along with retromer protein localization in T. vaginalis.

Cytidine nucleoside analog is an effective antiviral drug against Trichomonasvirus

BACKGROUND

Trichomonas vaginalis is the causative agent of a sexually transmitted disease in humans. The virulence of the parasite depends on multiple factors, including the presence of endosymbiotic dsRNA viruses. The presence of Trichomonasviruses (TVV) was associated with more severe genital symptoms, increased proinflammatory host reactions, and modulated parasite sensitivity to metronidazole. However, no efficient antiviral drugs are available against TVV to derive isogenic TVV-positive and TVV-negative cell lines that are essential for investigations of the TVV impact on T. vaginalis biology.

METHODS

7-Deaza-2'-C-methyladenosine (7d2CMA) and 2'-C-methylcytidine (2CMC) were used for TVV inhibitory assay. TVV replication was monitored using quantitative reverse transcription PCR (RT qPCR) and western blotting. Modeling of TVV1 RNA-dependent RNA polymerase (RdRp) was performed to visualize the inhibitor-RdRp interaction. Susceptibility to metronidazole was performed under aerobic and anaerobic conditions.

RESULTS

We demonstrated that 2CMC but not 7d2CMA is a potent inhibitor of TVV replication. Molecular modeling suggested that the RdRp active site can accommodate 2CMC in the active triphosphate nucleotide form. The effect of 2CMC was shown on strains infected with a single and multiple TVV species. The optimal 2CMC concentration (10 μM) demonstrated strong selectivity for TVVs over trichomonad growth. The presence of TVV has no effect on T. vaginalis metronidazole susceptibility in derived isogenic cell lines.

CONCLUSIONS

2CMC acts against TVVs and represents a new inhibitor against Totiviridae viruses. Our isogenic clones are now available for further studies of various aspects of T. vaginalis biology related to TVV infection.

Dynamic secretome of Trichomonas vaginalis: Case study of β-amylases

The secretion of virulence factors by parasitic protists into the host environment plays a fundamental role in multifactorial host-parasite interactions. Several effector proteins are known to be secreted by Trichomonas vaginalis, a human parasite of the urogenital tract. However, a comprehensive profiling of the T. vaginalis secretome remains elusive, as do the mechanisms of protein secretion. In this study, we used high-resolution label-free quantitative MS to analyze the T. vaginalis secretome, considering that secretion is a time- and temperature-dependent process, to define the cutoff for secreted proteins. In total, we identified 2 072 extracellular proteins, 89 of which displayed significant quantitative increases over time at 37 °C. These 89 bona fide secreted proteins were sorted into 13 functional categories. Approximately half of the secreted proteins were predicted to possess transmembrane helixes. These proteins mainly include putative adhesins and leishmaniolysin-like metallopeptidases. The other half of the soluble proteins include several novel potential virulence factors, such as DNaseII, pore-forming proteins, and β-amylases. Interestingly, current bioinformatic tools predicted the secretory signal in only 18% of the identified T. vaginalis-secreted proteins. Therefore, we used β-amylases as a model to investigate the T. vaginalis secretory pathway. We demonstrated that two β-amylases (BA1 and BA2) are transported via the classical endoplasmic reticulum-to-Golgi pathways, and in the case of BA1, we showed that the protein is glycosylated with multiple N-linked glycans of Hex5HexNAc2 structure. The secretion was inhibited by brefeldin A but not by FLI-06. Another two β-amylases (BA3 and BA4), which are encoded in the T. vaginalis genome but absent from the secretome, were targeted to the lysosomal compartment. Collectively, under defined in vitro conditions, our analysis provides a comprehensive set of constitutively secreted proteins that can serve as a reference for future comparative studies, and it provides the first information about the classical secretory pathway in this parasite.

The genetic diversity of metronidazole susceptibility in Trichomonas vaginalis clinical isolates in an Egyptian population

Trichomoniasis is the most common curable sexually transmitted disease worldwide. Resistance to metronidazole in treating trichomoniasis is a problematic health issue. We aimed to determine the minimum lethal concentration (MLC) of metronidazole for Trichomonas vaginalis isolates detected in Mansoura, Egypt and studied the genotypic profile of these isolates. Vaginal swab specimens were obtained from 320 symptomatic and 100 asymptomatic females, for whom clinical examination, vaginal discharge wet mount, Giemsa stain, and culture in modified Diamond's media were performed. Metronidazole susceptibility testing by an aerobic tube assay was performed. Both sensitive and resistant isolates were examined by PCR amplification followed by restriction fragment length polymorphism (RFLP). Trichomonas vaginalis was identified in 49/420 (11.7%) using either culture or PCR, while wet mount and Giemsa stain detected the parasite in 8.1 and 7.6% of participants, respectively. After 48 h incubation, most isolates were sensitive to metronidazole with a minimal lethal concentration (MLC) of 1 μg/ml. Mild resistance was observed in two isolates with MLCs of 64 μg\ml and mild to moderate resistance was observed in an additional two isolates with MLCs of 128 μg/ml. The four isolates that demonstrated low to moderate metronidazole resistance displayed a unique genotype band pattern by RFLP compared to the other 45 samples that were metronidazole sensitive. Our results highlight the presence of in vitro metronidazole tolerance in a few T. vaginalis isolates in Mansoura, Egypt that may lead to the development of drug resistance as well as the possibility of an identifying RFLP pattern in the isolates.

Trichomonas vaginalis contact-dependent cytolysis of epithelial cells

Trichomonas vaginalis is an extracellular protozoan parasite that binds to the epithelium of the human urogenital tract during infection. In this study, we examined the propensities of 26 T. vaginalis strains to bind to and lyse prostate (BPH-1) and ectocervical (Ect1) epithelium and to lyse red blood cells (RBCs). We found that only three of the strains had a statistically significant preference for either BPH-1 (MSA1103) or Ect1 (LA1 and MSA1123). Overall, we observed that levels of adherence are highly variable among strains, with a 12-fold range of adherence on Ect1 cells and a 45-fold range on BPH-1 cells. Cytolysis levels displayed even greater variability, from no detectable cytolysis to 80% or 90% cytolysis of Ect1 and BPH-1, respectively. Levels of adherence and cytolysis correlate for weakly adherent/cytolytic strains, and a threshold of attachment was found to be necessary to trigger cytolysis; however, this threshold can be reached without inducing cytolysis. Furthermore, cytolysis was completely blocked when we prevented attachment of the parasites to host cells while allowing soluble factors complete access. We demonstrate that hemolysis was a rare trait, with only 4 of the 26 strains capable of lysing >20% RBCs with a 1:30 parasite/RBC ratio. Hemolysis also did not correlate with adherence to or cytolysis of either male (BPH-1)- or female (Ect1)-derived epithelial cell lines. Our results reveal that despite a broad range of pathogenic properties among different T. vaginalis strains, all strains show strict contact-dependent cytolysis.

Alternative pathway of metronidazole activation in Trichomonas vaginalis hydrogenosomes

Metronidazole and related 5-nitroimidazoles are the only available drugs in the treatment of human urogenital trichomoniasis caused by the protozoan parasite Trichomonas vaginalis. The drugs are activated to cytotoxic anion radicals by their reduction within the hydrogenosomes. It has been established that electrons required for metronidazole activation are released from pyruvate by the activity of pyruvate:ferredoxin oxidoreductase and transferred to the drug by a low-redox-potential carrier, ferredoxin. Here we describe a novel pathway involved in the drug activation within the hydrogenosome. The source of electrons is malate, another major hydrogenosomal substrate, which is oxidatively decarboxylated to pyruvate and CO2 by NAD-dependent malic enzyme. The electrons released during this reaction are transferred from NADH to ferredoxin by NADH dehydrogenase homologous to the catalytic module of mitochondrial complex I, which uses ferredoxin as electron acceptor. Trichomonads acquire high-level metronidazole resistance only after both pyruvate- and malate-dependent pathways of metronidazole activation are eliminated from the hydrogenosomes.

Concordance between genetic relatedness and phenotypic similarities of Trichomonas vaginalis strains

BACKGROUND

Despite the medical importance of trichomoniasis, little is known about the genetic relatedness of Trichomonas vaginalis strains with similar biological characteristics. Furthermore, the distribution of endobionts such as mycoplasmas or Trichomonas vaginalis virus (TVV) in the T. vaginalis metapopulation is poorly characterised.

RESULTS

We assayed the relationship between 20 strains of T. vaginalis from 8 countries using the Random Amplified Polymorphic DNA (RAPD) analysis with 27 random primers. The genealogical tree was constructed and its bootstrap values were computed using the program FreeTree. Using the permutation tail probability tests we found that the topology of the tree reflected both the pattern of resistance to metronidazole (the major anti-trichomonal drug) (p < 0.01) and the pattern of infection of strains by mycoplasmas (p < 0.05). However, the tree did not reflect pattern of virulence, geographic origin or infection by TVV. Despite low bootstrap support for many branches, the significant clustering of strains with similar drug susceptibility suggests that the tree approaches the true genealogy of strains. The clustering of mycoplasma positive strains may be an experimental artifact, caused by shared RAPD characters which are dependent on the presence of mycoplasma DNA.

CONCLUSIONS

Our results confirmed both the suitability of the RAPD technique for genealogical studies in T. vaginalis and previous conclusions on the relatedness of metronidazol resistant strains. However, our studies indicate that testing analysed strains for the presence of endobionts and assessment of the robustness of tree topologies by bootstrap analysis seem to be obligatory steps in such analyses.

Resistance of Trichomonas vaginalis to metronidazole: report of the first three cases from Finland and optimization of in vitro susceptibility testing under various oxygen concentrations

Trichomonas vaginalis is a globally common sexually transmitted human parasite. Many strains of T. vaginalis from around the world have been described to be resistant to the current drug of choice, metronidazole. However, only a few cases of metronidazole resistance have been reported from Europe. The resistant strains cause prolonged infections which are difficult to treat. T. vaginalis infection also increases the risk for human immunodeficiency virus transmission. We present a practical method for determining the resistance of T. vaginalis to 5-nitroimidazoles. The suggested method was developed by determining the MICs and minimal lethal concentrations (MLCs) of metronidazole and ornidazole for T. vaginalis under various aerobic and anaerobic conditions. Using this assay we have found the first three metronidazole-resistant strains from Finland, although the origin of at least one of the strains seems to be Russia. Analysis of the patient-derived and previously characterized isolates showed that metronidazole-resistant strains were also resistant to ornidazole, and MLCs for all strains tested correlated well with the MICs. The suggested MICs of metronidazole for differentiation of sensitive and resistant isolates are >75 microg/ml in an aerobic 24-h assay and >15 microg/ml in an anaerobic 48-h assay.

Trichomonads, hydrogenosomes and drug resistance

Trichomonas vaginalis and Tritrichomonas foetus are sexually transmitted pathogens of the genito-urinary tract of humans and cattle, respectively. These organisms are amitochondrial anaerobes possessing hydrogenosomes, double membrane-bound organelles involved in catabolic processes extending glycolysis. The oxidative decarboxylation of pyruvate in hydrogenosomes is coupled to ATP synthesis and linked to ferredoxin-mediated electron transport. This pathway is responsible for metabolic activation of 5-nitroimidazole drugs, such as metronidazole, used in chemotherapy of trichomoniasis. Prolonged cultivation of trichomonads under sublethal pressure of metronidazole results in development of drug resistance. In both pathogenic species the resistance develops in a multistep process involving a sequence of stages that differ in drug susceptibility and metabolic activities. Aerobic resistance, similar to that occurring in clinical isolates of T. vaginalis from treatment-refractory patients, appears as the earliest stage. The terminal stage is characterised by stable anaerobic resistance at which the parasites show very high levels of minimal lethal concentration for metronidazole under anaerobic conditions (approximately 1000 microg ml(-1)). The key event in the development of resistance is progressive decrease and eventual loss of the pyruvate:ferredoxin oxidoreductase so that the drug-activating process is averted. In T. vaginalis at least, the development of resistance is also accompanied by decreased expression of ferredoxin. The pyruvate:ferredoxin oxidoreductase deficiency completely precludes metronidazole activation in T. foetus, while T. vaginalis possesses an additional drug-activating system which must be eliminated before the full resistance is acquired. This alternative pathway involves the hydrogenosomal malic enzyme and NAD:ferredoxin oxidoreductase. Metronidazole-resistant trichomonads compensate for the hydrogenosomal deficiency by an increased rate of glycolysis and by changes in their cytosolic pathways. Trichomonas vaginalis enhances lactate fermentation while T. foetus activates pyruvate conversion to ethanol. Drug-resistant T. foetus also increases activity of the cytosolic NADP-dependent malic enzyme, to enhance the pyruvate producing bypass and provide NADPH required by alcohol dehydrogenase. Production of succinate by this species is abolished. Metabolic changes accompanying in-vitro development of metronidazole resistance demonstrate the versatility of trichomonad metabolism and provide an interesting example of how unicellular eukaryotes can adjust their metabolism in response to the pressure of an unfavorable environment.

Failure of mebendazole to cure trichomonal vaginitis resistant to metronidazole: case reports

After a recent report showing the in vitro susceptibility to mebendazole of a strain of Trichomonas vaginalis that was resistant to metronidazole, we present two cases of metronidazole resistant infection, both of which failed to respond to oral mebendazole.

Trichomonal vaginitis refractory to treatment: case report

A woman initially aged 25 was treated for seven years for symptomatic vaginal trichomoniasis. Throughout that period the patient received 5-nitroimidazoles at conventional and high dosages, antimicrobial agents to eliminate vaginal organisms capable of interfering with treatment, acidifying preparations, and vaccination with inactivated Lactobacillus acidophilus. Despite all the regimens used, the condition remained refractory to treatment.

Anti-Trichomonas vaginalis monoclonal antibodies inducing complement-dependent cytotoxicity

Hybridomas producing monoclonal antibodies (mAbs) directed against Trichomonas vaginalis (Tv) have been produced in three fusions using mice immunized with live or killed Tv. The ELISA technique was used to test the binding activity of six out of the 48 mAbs produced. It was found that acetone fixation enhanced the binding activity of the antibodies and revealed hidden antigenic determinants. Thirty percent of the mAbs obtained from splenocytes of mice immunized with live Tv were of the IgG3 subtype. Two mAbs of the IgM and IgG3 subtypes demonstrated complement-fixing capacity. Incubation of these mAbs with live Tv and complement at 37 degrees for 30 min lysed the parasites. The lytic process was complement-dependent since in its absence the antibodies only agglutinated the parasites. The mAbs, when partially purified from ascitic fluids, had the same lytic activity as the native preparation. MAbs of the IgG1 subtype which did not fix complement, bound to Tv but did not lyse it. The lytic activity of the mAbs was not inhibited by cervico-vaginal secretions obtained from 14 women. It is suggested that mAbs could be used for diagnostic as well as for therapeutic purposes.

The dsRNA of Trichomonas vaginalis is associated with virus-like particles and does not correlate with metronidazole resistance

Twelve metronidazole-resistant and twelve metronidazole-susceptible strains of Trichomonas vaginalis were tested for the presence of dsRNA. Three resistant and five susceptible strains were found to contain dsRNA which indicated that metronidazole resistance does not correlate with the absence of dsRNA. Electron microscopy showed the homogenates of all dsRNA-positive strains to contain virus-like particles 32-38 nm in diameter, while no such particles were found in the dsRNA-negative strains. A mutual relationship between the dsRNA and virus-like particles seems to exist.

Viability of Trichomonas vaginalis in vitro at four temperatures

The effect of temperature as a possible factor on the survival of Trichomonas vaginalis for shipment or routine laboratory maintenance was studied. Ten strains of T. vaginalis, ATCC 30001, ATCC 30238, and eight clinical isolates, were examined for viability when kept incubated at 37 degrees C or removed from this temperature and held at 42, 22, or 5 degrees C for increasing lengths of time without subculture or reincubation at 37 degrees C. The order in which the strains remained viable without subculture was: 5 degrees C, 8 to 10 days; 22 degrees C, 4 to 8 days; 37 degrees C, 4 to 6 days; 42 degrees C, less than 2 days. Vials of medium with cells were also held at 22 and 5 degrees C and then reincubated at 37 degrees C. Cultures held at 22 degrees C remained viable 6 to 8 days, whereas those stored at 5 degrees C remained viable 10 to 14 days. These data show that T. vaginalis withstands a wide range of temperatures, particularly below normal growth temperatures without subcultures, beyond what would be expected in mailing cultures.