Figure 1.

Influence of starting parasitaemia of P. knowlesi (A1-H.1) and P. falciparum (3D7) on assay quality for both the fluorescent and colorimetric methods. Parasites set to 1% haematocrit and varying parasitaemia (0.1%–2%) were cultured in the presence or absence of a supralethal concentration of chloroquine for 27 h (circles), 54 h (squares) or 81 h (diamonds) for P. knowlesi, and 48 h (cirlces) or 96 h (squares) for P. falciparum. Upon termination of the assay, the plates were read using either the SYBR Green I fluorescence assay (a, c, e and g) or the LDH assay (b, d, f and h). The signal window and Z′ factor were calculated for each assay. The signal window was calculated by dividing the average reading for the drug-free control by the average reading for the high chloroquine concentration (background) control. The assay quality was assessed by determining the Z′ factor using the formula described in Zhang et al.¹⁷