A cta Troptca, 49( 1991)201-213 201 Elsevier ACTROP 00149 The effect of diminazene aceturate and isometamidium chloride on cultured procyclic forms of susceptible and drug-resistant Trypanosoma congolense I.E. Elrayah and R. Kaminsky lnternatwnal Laboratory for Research on Amrnal Diseases (ILRAD), Nazrobt, Kenya (Received 15 October 1990, accepted 17 January 1991) Cultures of insect forms of Trypanosorna congolense stocks and clones with different susceptlbthtles to trypanocldal drugs m VlVO were m~tmted from bloodstream trypomastlgotes harvested from mammahan hosts and malntamed axenlcally m vitro at 27~C Growth inhibition of procychc forms of susceptible and drug-resistant T congolense occurred after incubation for 48 h with 0 1 ng lsometamldlum chlonde/ml or 500 ng dlmmazene aceturate/ml Procychc forms were propagated in wtro m the presence of 10 or 100 ng dlmmazene aceturate/ml for 20 days without or with only minor loss of growth In the presence of 0 1 or 1 ng lsometamldmm chlonde/ml the trypanocldal effect was detectable after 6-8 days and the cultures died after 10-12 days Concentrations of 1 or I0 ng isometamldmm chlonde/ml had an lrreversxbleeffect when the trypanosomes were exposed to the drug for 24 h Both drugs used m this study thus showed antltrypanosomal actw~ty on T congolense procychc forms but ~t was not possible to distinguish between drug-resistant and susceptible stocks or clones employmg the cnterm of growth inhibition or death of trypanosomes m culture Key words Trvpanosoma congolense, Drug resistance, in vitro, Isometamldmm chloride, Dlmmazene aceturate Introduction Extenswe use of the limited number of commercially avadable drugs for the control of ammal trypanosomlasls has resulted m the appearance of drug-resistant trypano- somes m West (Authle, 1984, Joshua, 1988) and East Africa (Gltatha, 1979, Rottcher and Schllhnger, 1985, Schflhnger, 1985, Mbwambo et al, 1988). Improved surved- lance of drug resistance reqmres rapid, inexpensive and rehable techmques for identification of drug-resistant trypanosomes Assessment of drug suscept~bdlty of a particular trypanosome population is at present done by mouse inoculation followed by treatment using the drug m question. In seekmg alternatives, in vitro techniques have been examined for their usefulness for assessing drug susceptlblhtles Ant~trypanosomal actwlty of drugs can be observed m in vitro culture conditions Correspondence address R Kammsky, ILRAD, P O Box 30709, Nalrobl, Kenya 0001-706X/91/$03 50 © 1991 Elsevier Science Pubhshers B V