Host serum modifies the drug susceptibility of Babesia bovis in vitro.

Babesia parasites generally require a defined percentage of serum in the culture medium for their in vitro growth. In this study, we attempted to culture Babesia bovis in a serum-free condition. The growth pattern and morphology of B. bovis in serum-free (plain) GIT medium were unaltered as compared to those of the standard growth condition containing 40% bovine serum in M199. When exposed to the test drugs, the parasite in plain GIT medium showed clearly lower IC 50 values than those in 40% serum-containing GIT medium, indicating that several serum components may interfere with the drug bio-availability. Therefore, the serum-free culture system is useful for standardizing drug test protocols and understanding the roles of serum factors in the drug test.