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Abstract
Doxycycline sensitivity against in vitro cultured Babesia gibsoni was evaluated by real-time PCR and parasitemia.
The culture of B. gibsoni was successfully continued and mean parasitemia was 4.63% when in vitro drug sensitivity
test was started. The drug sensitivity test by the real-time PCR calculated the gene copy number from cultured
sample. Even if the complete growth inhibition was at certain concentration, the genomic DNA might remain in
existence. The results revealed that the doses of doxycycline 8µM, 16 µM, 32 µM and 64 µM of both real-time PCR
and parasitemia inhibited the growth of B. gibsoni in a dose-dependent manner at 96 h and 144 h. We determined
the IC50 of doxycycline 17.9 µM at 96 h and 13.8 µM at 144 h after treatment using real-time PCR. Morphological
observation revealed that the number of parasites decreased per erythrocyte and line shaped parasites increased in
erythrocytes with the increased concentration of doxycycline. Doxycycline effectively inhibits the growth of B. gibsoni
in vitro. Therefore, doxycycline can be used to treat B. gibsoni infection. Further studies are important to know the
doxycycline resistance in B. gibsoni.