Development and characterization of a strain of Babesia gibsoni resistant to diminazene aceturate in vitro.

We attempted to develop a strain of Babesia gibsoni resistant to diminazene aceturate (DA), an anti-babesial drug, in vitro. Since the DA-sensitive B. gibsoni strain could survive and proliferate in culture medium containing 1 ng/m l DA, the concentration of DA was gradually increased from 1 to 200 ng/ml. The results showed that the parasites could survive and proliferate in the medium containing 200 ng/m l DA, which was much higher than the 50% inhibitory concentration (IC(50)) of DA for B. gibsoni. Subsequently, these parasites were removed from erythrocytes and exposed directly to 200 ng/ml DA. They were able to survive and invade fresh erythrocytes, though the DA-sensitive B. gibsoni strain did not survive. Based on these results, the parasites cultured within 200 ng/ml DA were determined to be a DA-resistant B. gibsoni strain. In addition, the IC(50) levels of clindamycin, doxycycline and pentamidine for the DA-resistant B. gibsoni strain were determined. The IC(50) levels of clindamycin, doxycycline and pentamidine for the DA-resistant strain were higher than those for the DA-sensitive strain. The IC(50) of pentamidine for the resistant strain was much greater than that for the DA-sensitive strain. These results indicated that the DA-resistant B. gibsoni strain could have resistance not only to DA, but also to other anti-babesial drugs. In conclusion, we successfully developed a DA-resistant B. gibsoni strain in vitro.