The inhibitory properties and mode of action of plant essential oils and fruit extracts on protozoan parasites

Abstract

The main aims and objectives of this study was to determine if plant essential oils (PEOs) and polyphenol-rich fruit extracts (PRFEs) could reduce the viability of Giardia duodenalis trophozoites, Trypanosoma cruzi epimastigotes and Cryptospordium parvum oocysts in vitro. All PEOs tested reduced epimastigote and trophozoite viability at a concentration of 0.02% v/v, with titrations of the PEOs showing a concentration dependant decrease in viability. The minimum inhibitory concentrations (MICs) of PEOs demonstrated that myrtle and elemi oil were the most active PEOs (trophozoites = 0.005% v/v; epimastigotes = 0.00125% v/v) with the terpenes, α-pinene and limonene, constituents of these oils, being responsible for their action. Incubation of palmarosa oil and its terpene, geraniol, with C. parvum oocysts caused the almost complete excystation of oocysts (in the presence of increased temperature and time), with geranium oil and its terpene, citronellol, being nearly as effective. PRFEs reduce trophozoite viability, with 4 members of the Rosaceae Family causing complete reduction at 167 μg ml-1, possibly through their ellagitannin content. Cloudberry extract was found to have an MIC comparable to the drug metronidazole (67 μg ml-1). The historical use of blueberries for the treatment of diarrhoeal diseases was demonstrated by the ability of blueberry PRFE, pressed juice and drink to kill trophozoites. Protein expression was both inhibited and upregulated in several proteins in whole cell lysates of PEO treated trophozoites, indicating a supplemental intracellular mode of action. Both PEOs and PRFEs cause morphological changes to epimastigotes and trophozoites through flagellar truncation and internalisation, swelling and rounding of the cell body, cytoplasmic condensation and the formation of large membrane protrusions. These indicate an action on the membrane itself with possible changes in osmoregulation. Both PEOs and PRFEs can be considered to be candidates for novel drug discovery for the treatments of cryptosporidiosis, giardiasis and American trypanosomiasis.