Evaluating the Effect of Selected Medicinal Plant Extracts and their Synergistic Effect with Metronidazole against Entamoeba histolytica

Introduction: Intestinal infection with Entamoeba histolytica is an important cause of diarrhoea world-wide especially where sanitation conditions are poor. Medicinal plants have played a significant role in various traditional systems of medications including intestinal infections caused by E. histolytica. Objectives: To investigate the antiamoebic activity of pomegranate, castor and thyme aqueous and alcoholic extracts, in addition to thyme oil and pomergnate juice against E. histolytica and to determine the synergistic effect of these plant extracts with the antibiotic metronidazole. Methods: Three medicinal plants pomegranate (Punica granatum), castor (Ricinus communis L) and thyme (Thymus vulgaris L) were used in this study. Some of these plants were bought from fruit's market in Gaza and some were collected from some regions in Gaza; each plant was dried then extracted according to standard extraction method using Soxhlet apparatus. E. histolytica was cultured in a modified diphasic liver infusion agar medium in vitro conditions to study the effect of these plant extracts on E. histolytica and their synergestic effect with the antibiotic metronidazole. The type of E. histolytica was confirmed using PCR. Results: Successful cultures of E. histolytica were obtained. All the plant materials used in this study possessed antiamoebic activity in vitro with different levels except the aqueous extract of R. communis leaves which also was the only one didn’t show synergistic effect with metronidazole at tested concentrations. Alcoholic extract of P. granatum pulp had the strongest antiamoebic activity with MIC of < 5 mg/ml while the aqueous extract of T. vulgaris leaves had the weakest antiamoebic activity with a MIC of < 20 mg/ml. Oils and Juice: P. granatum juice possessed antiamoebic activity and synergistic effect with a MIC < 12.5 % (v/v). T. vulgaris oil not only possessed antiamoebic activity and synergistic effect but also had the strongest activity and a MIC of < 6.5% (v/v), and the best synergistic effect. Metronidazole is still effective against E. histolytica with a MIC < 20 µg/ml and exhibit greater amoebicidal activity as compared with the plant extracts. It is recommended that pomegranate and thyme should be advised by physicians to treat E. histolytica infection with or without metronidazole. The plant extracts which showed a good amoebicidal activity in vitro should be tested in vivo on experimental animals to evaluate their amoebicidal effect and their synergistic effect with metronidazole on E. histolytica and also recommended to raise awareness regarding the use of medicinal plants to treat parasitic infections