In vitro antiprotozoal activity of some medicinal plants methanolic extracts against Entamoeba histolytica and Giardia lamblia

This study aimed to investigate the in vitro antiprotozoal effects of methanolic seed extracts of the Ruta graveolens, Peganum harmala, and Citrullus colocynthis against Giardia lamblia and Entamoeba histolytica using the trypan blue staining method and MTT Assay. Cultured trophozoites of G. lamblia and E. histolytica were treated with 20 µg/mL of Metronidazole (MTZ) and 40 mg/mL of R. graveolens, P. harmala, and C. colocynthis seed extracts. Metronidazole significantly reduced the number of living G. lamblia and E. histolytica trophozoites (P < 0.05) as compared to the negative control (normal saline). R. graveolens significantly showed better effects on the mortality rate of both G. lamblia, and E. histolytica trophozoites in comparison to P harmala (P < 0.05) followed by C. colocynthis (P < 0.05) by using both colorimetric and trypan blue methods, whereas IC₅₀ in all plants extracts was >40 mg/mL. Among the tested plant extracts, R. graveolens showed significant antiprotozoal activity against G. lamblia and E. histolytica trophozoite in vitro but far less than metronidazole, a drug used as a positive control. The results of the antiprotozoal screening support the possible use of R. graveolens for the treatment of diarrhea and dysentery in the traditional medicine.