ABSTRACT
Background: Blastocystis spp. Are protozoan parasites that cause a wide range of gastrointestinal manifestations and in is incriminated of being a possible element in the development of irritable bowel diseases as well as colorectal carcinoma. Metronidazole (MTZ) is commonly prescribed for treatment of blastocystosis. However, the reported increase in MTZ resistance parasites and undesirable side effects make the search for an alternative a priority. Syzygium aromaticum-eugenol rich  essential oil has been wiedly investigated for its medicinal properties.
 
Objective: The present study was carried out to investigated the vitro effects of S.aromaticum-eugeonl rich essential oil on Blastocystis spp.in vitro.
 
Material and Methods:  Stool samples were collected from patients complaining of diarrhea, referred for stool examination to the research and diagnostic laboratory unit of the parasitology department, Faculty of Medicine, Ain Shams University. Microscopically, positive stool samples for Blastocystis spp.  Were cultured. Compared with MTZ, the effects of different concentrations of S.aromaticum essential oil on the viability of Blastocystis spp., tested essential oil, MTZand untreated parasite control was measured.
Results: The minimal lethal concentrations for S.aromaticum were 300 μg/ml at 24h, 200 μg/ml at 48h, 100 μg/ml at 72h and 50 μg/ml at 96h, as compared to MTZ 1mg/ml that did not induce complete inhibition till the end of the studied intervals. Notable shrinkage in the size of Blastocystis-treated with S.aromaticum, was significantly smaller than that of parasite control.
Conclusion: These results highly suggest that S.aromaticum essential oil may be a promising and safe agent for treatment of blastocystis.