EVMSPJ. Vol.9 ((2013) Elbadr,etal. _______________________________________________________________________________________ 12 Antiprotozoal activity of Rosmarinus officinalis and Ocimum basilicum against Giardia lamblia A. M. Elbadr 1 , U. M. Abdul. Raouf 2 , N. F. Abo- Dahab 3 , Dr. Salah G. A. Badr 4 and Ashraf kh. Abd Elghany 5 1- Dep. of Parasitology Faculty of Medicine Assuit University. 2,3,&4-Dep. of Microbiology Faculty of Science of Al-Azhar University (Assuit). 5- Research scholar , Specialist medical Laboratory at the Institute of Oncology Sohag. Corresponding author: ashrrrrf_2008@yahoo.com 5 Abstract Giardiasis is worldwide spread disease caused by the protozoan several Giardia species. Its treatment includes drugs which may produce side effects and, in addition, onset of chemical resistance of this pathogenic protozoan. Thus, with the purpose of searching for new natural anti-protozoal chemotherapy, two plants of the family Lamiaceae, Rosmarinus officinalis and Ocimum basilicum used in traditional medicine against intestinal disorders were selected to evaluate their petroleum ether, ethyl acetate, methanol and aqueous leaves extracts activity against G.lamblia trophozoite. Pet. Ether extract from R. officinalis was strongly active against G. lamblia (IC50 = 4.382 mg ml -1 ) and good activity of O. basilicum (IC50 = 14.9 mg ml - 1 ). Ethyl acetate extract from R. officinalis was strongly active against G. lamblia (IC50 = 2.02 mg ml -1 ) and moderate activity of O. basilicum (IC50 = 25.4 mg ml -1 ). Methanol extract from R. officinalis was strongly active against G. lamblia (IC50 = 2.383 mg ml -1 ) and moderate activity of O. basilicum (IC50 = 33.8 mg ml -1 ). None of the aqueous extracts of the two plants were active against tested protozoan. Such results indicate R. officinalis ethyl acetate extract and petroleum ether extract from O. basilicum as possible candidates for further investigations to isolate and characterize their active principles as possible new natural anti-protozoal agents. Keywords: Rosmarinus officinalis; Ocimum basilicum; Giardia lamblia. Introduction Giardiasis is worldwide distributed protozoal disease caused by Giardia lamblia. Giardiasis is considered the most common protozoan infection in humans with 20-60% incidence worldwide (Upcroft and Upcroft, 2001). Its treatment includes drugs as metronidazole, furazolidone, paromomycin, benzimidazoles, which may produce side effects; in addition, pathogenic protozoan developed resistance to some of them (Guerrant et al., 1999; Liu et al., 2000; Gardner and Hill, 2001). Carcinogenic, teratogenic and embryotoxic properties have also been documented for some of these products (Upcroft and Upcroft, 2001). Medicinal plants represent natural therapeutic alternatives against pathogenic microorganisms, being safer than their synthetic counterparts. Lamiaceae family is used in traditional and folk medicine (Hedge, 1992). Rosemary (Rosmarinus officinalis L.) is a spice and medicinal herb widely used around the world. Of the natural antioxidants, rosemary has been widely accepted as one of the spices with the highest antioxidant activity (Peng et al., 2005). The main compounds responsible for the antimicrobial activity are α-pinene, bornyl acetate, camphor and 1,8-cineole (Daferera et al., 2000; Pintore et al., 2002). Its herb and oil are commonly used as spice and flavoring agents in food processing for its desirable flavor, high antioxidant activity and lately as antimicrobial agent (Ouattara et al., 1997). Ocimum basilicum, known as Rahan in Al-Madinah is used as carminative, expectorant, stimulant and diaphoretic. Leaf juice is traditionally used to treat cough, fever, ringworm, internal piles, diarrhea and kidney disorders (Mossa et al., 2000). Its essential oils showed antimicrobial activity against Gram- negative and Gram-positive bacteria, yeasts, and molds (Suppakul et al., 2003). Thus, with the purpose of searching for new natural anti-protozoal chemotherapy, two plants of the family Lamiaceae R. officinalis and O. basilicum used in traditional medicine against intestinal disorders were selected to evaluate their petroleum ether, ethyl acetate, methanol and aqueous leaves extracts activity