Influence of medium composition on erythrocyte invasion efficiency. The invasion assays were performed in 3 basic media (white bars), and compared to the complete medium (gray bar). CaCl2 (striped bars) or MgCl2 (black bars) were added at a concentration of 1 mM into the basic media separately. Each figure represents the average value of parasitemia from the triplicate assays and error bars indicate the standard deviation. Significant differences (P < 0.05) between complete medium and basic media are indicated with stars, while significant differences due to addition of calcium of magnesium in each basic medium are indicated with crosses.