Isolation of Trichomonas vaginalis resistant to metronidazole

Biochemical and structural characterization of beta-carbonic anhydrase from the parasite Trichomonas vaginalis

Abstract

Trichomonas vaginalis is a unicellular parasite and responsible for one of the most common sexually transmittable infections worldwide, trichomoniasis. Carbonic anhydrases (CAs) are enzymes found in all lifeforms and are known to play a vital role in many biochemical processes in organisms including the maintenance of acid–base homeostasis. To date, eight evolutionarily divergent but functionally convergent forms of CAs (α, β, γ, δ, ζ, η, θ, and ι) have been discovered. The human genome contains only α-CAs, whereas many clinically significant pathogens express only β-CAs and/or γ-CAs. The characterization of pathogenic β- and γ-CAs provides important knowledge for targeting these biomolecules to develop novel anti-invectives against trichomoniasis. Here, we report the recombinant production and characterization of the second β-CA of T. vaginalis (TvaCA2). Light scattering analysis revealed that TvaCA2 is a dimeric protein, which was further supported with in silico modeling, suggesting similar structures between TvaCA2 and the first β-CA of T. vaginalis (TvaCA1). TvaCA2 exhibited moderate catalytic activity with the following kinetic parameters: k_cat of 3.8 × 10⁵ s⁻¹ and k_cat/K_M of 4.4 × 10⁷ M⁻¹ s⁻¹. Enzyme activity inhibition was studied with a set of clinically used sulfonamides and sulfonamide derivates. Twenty-seven out of the 39 compounds resulted in inhibition with a nanomolar range. These initial results encourage for future work entailing the design of more potent inhibitors against TvaCA2, which may provide new assets to fight trichomoniasis.

Key messages

• Protozoan parasite Trichomonas vaginalis has two β-carbonic anhydrases (TvaCA1/2).

• TvaCA1/TvaCA2 represents promising targets for antitrichomonal drug development.

• TvaCA2 is a dimer of 20.3 kDa and possesses moderate catalytic activity.

• The most efficient inhibitor was clinical drug acetazolamide with K_I of 222.9 nM.

• The 39 tested sulfonamides form the basis for the design of more potent inhibitors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-021-02148-1.

Biochemical and structural characterisation of a protozoan beta-carbonic anhydrase from Trichomonas vaginalis

We report the biochemical and structural characterisation of a beta-carbonic anhydrase (β-CA) from Trichomonas vaginalis, a unicellular parasite responsible for one of the world’s leading sexually transmitted infections, trichomoniasis. CAs are ubiquitous metalloenzymes belonging to eight evolutionarily divergent groups (α, β, γ, δ, ζ, η, θ, and ι); humans express only α-CAs, whereas many clinically significant pathogens express only β- and/or γ-CAs. For this reason, the latter two groups of CAs are promising biomedical targets for novel antiinfective agents. The β-CA from T. vaginalis (TvaCA1) was recombinantly produced and biochemically characterised. The crystal structure was determined, revealing the canonical dimeric fold of β-CAs and the main features of the enzyme active site. The comparison with the active site of human CA enzymes revealed significant differences that can be exploited for the design of inhibitors selective for the protozoan enzyme with respect to the human ones.

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.

[Effect of sodium nitrite on Trichomonas vaginalis]

We have investigated the action of sodium nitrite on the growth and morphologic changes of T. vaginalis and on the treatment of subcutaneous abscess by trichomonad in mice. Sodium nitrite inhibited the growth of metronidazole-sensitive KT9 isolate and metronidazole-resistant CDC85 strain of T. vaginalis as concentration of 6 mM and 10 mM, respectively. Intraperitoneal injection of sodium nitrite (70 micrograms, 100 micrograms, 130 micrograms/g body weight) did not reduce the size of abscess produced by subcutaneous inoculation of T. vaginalis in mice. T. vaginalis, treated with sodium nitrite at concentration giving about 50% inhibition of growth, showed fissures, many vacuoles and electron-translucent zone in the cytoplasm by transmission electron microscopy. In the case of CDC85 treated with 9 mM sodium nitrite, hydrogenosomal matrical change, destruction of hydrogenosomal membrane, autophagic vacuoles, disappearance of Golgi complex and polysome were notably observed. With above results, it is assumed that sodium nitrite inhibits the growth of metronidazole-sensitive and--resistant strains of T. vaginalis and induces the morphological changes of T. vaginalis although it does not affect in reducing of abscess size by T. vaginalis in mice.

An investigation, by questionnaire, of cases of recalcitrant vaginal trichomoniasis seen in genitourinary medicine clinics in the United Kingdom. British Co-operative Clinical Group

A total of 24 cases of recalcitrant trichomoniasis were reported from 18 centres widely scattered throughout the UK. Most cases had received numerous courses of unsuccessful treatment. Nine (75%) of 12 tested isolates had a decreased susceptibility to metronidazole. Local laboratories were often unable to evaluate fully trichomonal isolates and it is recommended that consideration be given to the establishment of a national reference laboratory. Although there were no universal cures, successful alternatives to conventional treatments are detailed.

In vitro effects of berberine sulphate on the growth and structure of Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis

The plant alkaloid, berberine sulphate, inhibited the growth of Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis in BI-S-33 medium, and induced morphological changes in the parasites. Exposure of E. histolytica to berberine caused a clumping of chromatin in the nucleus, and the formation of autophagic vacuoles and aggregates of small vacuoles in the cytoplasm. In berberine-treated G. lamblia, an irregularly-shaped vacuole appeared in the cytoplasm and gradually enlarged during culture. The trophozoites became swollen and deposits of glycogen were seen in the cytoplasm. Trichomonas vaginalis was also affected by the berberine; autophagic vacuoles increased in number soon after exposure, and one large vacuole, which was characteristic of treated cells, appeared. These observations demonstrate that, in vitro, this drug was effective against E. histolytica, G. lamblia and T. vaginalis. Another alkaloid, coptisine, was inactive against the three parasites.

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.

Managing trichomonal vaginitis refractory to conventional treatment with metronidazole

Three patients with vulvovaginitis caused by Trichomonas vaginalis, which was refractory to conventional treatment with metronidazole are described. The T vaginalis strain isolated from one patient was resistant to metronidazole (minimum inhibitory concentration (MIC) more than 100 mg/l) under aerobic conditions, although under anaerobic conditions it was as susceptible as a normal reference strain. The effect of the concomitant use of other medication and the influence of other vaginal pathogens on the efficacy of metronidazole are highlighted.

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

Six isolates of a strain (MRP-MT) of Trichomonas vaginalis obtained from a woman before and after unsuccessful treatment with metronidazole had an appreciably lower susceptibility to metronidazole both in vitro in the aerobic tube assay and in vivo in the mouse assay than did control strains from patients cured with standard doses of the drug. Our results support recent evidence that metronidazole-resistant strains of T vaginalis do cause treatment failure. Resistance of these strains could be detected in vitro under only aerobic but not anaerobic conditions. The prevalence of metronidazole-resistant strains of T vaginalis should be kept under surveillance in order to estimate their clinical importance. The patient harbouring the resistant strain MRP-MT was finally cured with increased doses of ornidazole.