In vitro responsiveness of Babesia bovis to imidocarb dipropionate and the selection of a drug-adapted line.

A South African stock of Babesia bovis was successfully resuscitated from liquid nitrogen, and cultured in microaerophilous stationary phase. The in vitro susceptibility of the B. bovis stock to titrated concentrations of imidocarb dipropionate was observed and the 50% inhibitory concentration (IC) was determined (8.7 x 10(7) g ml-1). A drug-adapted line was developed by culture in the presence of sub-inhibitory concentrations of imidocarb dipropionate and it had an IC50 eight times higher than that of its original stock (6.6 x 10(-6) g ml-1). The drug-adapted line was cryopreserved and resuscitated from liquid nitrogen. Continuous culture of the non-drug adapted line through 15 subcultures did not change the IC50 (8.3 x 10(-7) g ml-1).