Effect of in vitro cultivation on the stability of resistance of Trypanosoma brucei brucei to diminazene, isometamidium, quinapyramine, and Mel B.

A Trypanosoma brucei brucei stock resistant to diminazene aceturate, isometamidium chloride, quinapyramine sulfate, and Mel B was grown in vitro and its response to these drugs compared to that of a drug-sensitive trypanosome stock. There was little if any change of drug sensitivity after in vitro propagation as bloodstream forms for 120, 177, and 275 days and after in vitro transformation of bloodstream forms into procyclic, epimastigote, and finally metacyclic forms. Drug resistance was stable during in vitro maintenance in the absence of drugs in both culture systems. The response of resistant and sensitive T. b. brucei to diminazene in vitro correlated with their sensitivity pattern in vivo. Thus, in vitro techniques can be used to study drug resistance in trypanosomes. African trypanosomes of the subgenus Trypanozoon cause disease in both man and animals. At present, chemotherapy is the only possible cure for trypanosomiasis, and chemoprophylaxis of ruminants is a widely applied preventive measure. The appearance of trypanosome strains resistant to the limited number of trypanocides is an increasing problem for chemotherapy and chemoprophylaxis of livestock (Leach and Roberts, 1981; Roettcher and Schillinger, 1985; Abebe, 1987). To maintain drug-resistant trypanosomes in vitro would facilitate studies on their mechanisms of resistance. It is not known, however, whether in vitro cultivation of trypanosomes changes their sensitivity to drug treatment. To study this question, a multiresistant Trypanosoma brucei brucei stock was examined both before and after in vitro cultivation as bloodstream forms, and throughout all insect life stages (procyclics, epimastigotes, and metacyclics) in comparison to drug-sensitive trypanosomes. MATERIALS AND METHODS