Fig 4.

Cytocidal effects of PA-824 enantiomers on L. donovani promastigotes. The S (A) and the R (B) enantiomers of PA-824 were added to early-log-phase cultures of LdBOB promastigotes (∼1 × 10⁶ ml⁻¹) at concentrations equivalent to 10 times their respective EC₅₀s. At intervals, the cell densities were determined, and samples of culture (500 μl) were removed, washed, and resuspended in fresh culture medium in the absence of drug. The viability of washed parasites was monitored for up to 72 h following removal from drug exposure, and the point of irreversible drug toxicity was determined (skull and crossbones). Open circles, no inhibitor; filled circles, presence of drug.