Vero cells were harvested during exponential growth, cultured in 96-well plates (density= 12×104
cells/mL)
and incubated at 37ºC in 5 % CO2 incubator for 24 hr. Then, 6×105
parasites/mL of T.gondii parasite were
added to each well (parasite: cell ratio = 5:1, final volume 200 μL) [3]. Six hours after inoculation, the
cultures were washed twice with Dulbecco’s Modified Eagle Medium (DMEM) without Fetal bovine serum
(FBS) to remove any non-adherent parasites. After 18 hr incubation, DMEM medium was added to each well
along with serial concentrations of essential oil. After 24 hr of treatment, anti-T.gondii activity of nutmeg
essential oil was examined using the MTT assay [12] with some modifications. Clindamycin served as the
positive control. The assay was conducted in 96-well plates and assayed using a microplate reader using a
wavelength of 540 nm. All of the test compounds were assayed in triplicate at each concentration. All data
points represent the mean of three independent experiments. The percentage of growth inhibition (GI) was
calculated manually using the formula: