High priority has been given to new assays that facilitate and accelerate the development of novel antimalarial compounds. Unlike evaluation of drugs in vitro, in which new approaches have been used to expedite identification of parasites, the conventional in vivo murine assay requires determination of parasitemia by light microscopy, an incompatible technique to test large numbers of drugs. We have investigated the possibility of using an autonomously fluorescent Plasmodium berghei strain, stably transformed with the green fluorescent protein, to rapidly quantify parasite growth by flow cytometry. The major improvement of this method is that P. berghei line transformed with green fluorescent protein parasites can be quickly and specifically detected in a drop of parasite-infected blood without any manipulation of the sample. Our results showed a clear correlation between the numbers of fluorescent cells detected by flow cytometry and conventional parasitemia, including a correspondence in the peaks of parasitemia. The validation of P. berghei line transformed with green fluorescent protein for chemotherapy studies was performed by evaluating its response to conventional antimalarial drugs such as chloroquine, quinine and sodium artesunate. The results of drug-susceptibility assays as determined by flow cytometry were comparable with those obtained by microscopic examination of Giemsa-stained slides. This PbGFP parasite should prove to be a rapid, simple and sensitive tool for the examination of the large number of compounds and conditions involved in the initial stages of drug development. © 2003 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.
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