Blastocystis spp. is a protozoan parasite with controversial clinical significance and consensus 
for treatment. Metronidazole (MTZ) was considered the main line of treatment, but drug re
sistance and many side effects motivated the search for effective safe therapy. 
This study evaluated the in vitro therapeutic effects of aqueous extracts of nine Egyptian herbs 
on Blastocystis spp. compared to MTZ as standard control drug. 
Blastocystis-positive stool samples were obtained from patients with gastrointestinal symptoms 
by direct smears and FECT. Aqueous extract of herbal plants (A. sativum, N. sativa, P. nigrum, C. 
cyminum, Z. officinale, T. vulgaris, O. majorana, M. chamomilla & A. Judaica) were prepared.  
Positive samples were incubated with 0.1mg/ml concentration of tested herbal extracts on Jones 
medium at 37ºC versus 0.1mg/ml MTZ as a control. Parasite count was assessed after 24, 48, & 
72hr post incubation.  
The A. sativum, M. chamomilla, A. Judaica & N. sativa extracts showed highly significant gro
wth inhibition rate of Blastocystis species compared to MTZ followed by O. majorana, C. cymin- 
um & T. vulgaris extract. But, P. nigrum & Z. officinale extracts showed insignificant growth rate.