Clones of different sensitivities in drug-resistant isolates of Plasmodium falciparum.

Clones of two Thai isolates of Plasmodium falciparum were prepared and examined for variations in drug susceptibility and electrophoretic properties of enzymes. Both isolates were found to include mixtures of genetically distinct parasites. Of particular significance was the finding that one isolate (T(9)), which on initial testing was resistant to chloroquine, pyrimethamine and sulfadoxine-pyrimethamine, yielded a clone of parasites markedly more sensitive to these three drugs, while five other clones resembled the original isolate in drug susceptibility.