Exogenous Δ7-dafachronic acid promotes formation of Strongyloides stercoralis second-generation free-living larvae and blocks the formation of infective third-stage larvae.

Post-free-living larvae of S. stercoralis developing synchronously in agar plate cultures were exposed to increasing concentrations of Δ7-dafachronic acid (Δ7-DA). A) Frequency of development to rhabditiform post-free-living third- and fourth-stage larvae (FL L3-L4) as a function of Δ7-DA concentration. The sample denoted 0 nM Δ7-DA is the ethanol control. ** Positive correlation of FL L3-L4 frequency with Δ7-DA concentration is significant (P = 0.001; R2 = 0.902). B) Frequency of development to infective third-stage larvae (iL3) as a function of Δ7-DA concentration, with 0 nM Δ7-DA as the ethanol control. Negative correlation of iL3 frequency with Δ7-DA concentration is significant (P = 0.0135; R2 = 0.736). In both panels, bar height represents the mean of three biological replicates; error bars represent +1 standard deviation.