A new pharmacological screening assay with Trypanosoma cruzi epimastigotes expressing ?-galactosidase

We have developed a new pharmacological screening assay for epimastigotes of Trypanosoma cruzi (clone CL-B5) that express the Escherichia coli LacZ gene. The assay is based on determining the activity of the cytoplasmic beta-galactosidase released into the culture on membrane lysis in the presence of the substrate chlorophenol red beta-D-galactopyranoside (CPRG). The experimental conditions were adjusted to find those in which the relationship between epimastigote number and CPRG absorbance was linear over the widest possible range. Absorbance was significantly correlated with the number epimastigote from 5x10(3) to 1.2x10(6) parasites/ml (r=0.98, P