QUINACRINE-RESISTANT GIARDIA-DUODENALIS

Quinacrine resistance has been induced in 3 Giardia duodenalis laborat ory stocks and 4 lines resistant to other drugs. The quinacrine-resist ant lines were maintained in normally lethal levels of 5 mu M quinacri ne and some lines are viable in 20 mu M levels of the drug. Fluorescen ce studies indicated that quinacrine was taken up by sensitive cells b ut was actively excluded from resistant trophozoites. The nuclei were not a site of drug accumulation and no specific fluorescence in the tr ophozoite could be attributed to any structure. Blebs of concentrated drug appeared prior to disintegration of the membrane of drug-sensitiv e trophozoites exposed to drug overnight. Parasite lines already resis tant to furazolidone adapted more readily to quinacrine exposure than drug-sensitive stocks. This multiple drug resistant phenotype was not as marked with metronidazole-resistant lines.