A Cytophaga-like organism (CLO), isolated from the tick Ixodes scapularis (IsCLO), was adapted to growth in insect cell lines and its antibiotic sensitivity was tested. IsCLO were introduced to four insect cell lines, and their growth was measured by quantitative polymerase chain reaction. IsCLO propagated well in a mosquito cell line, AeAl-2, and caused cytopathic effects in host cells. A lepidopteran cell line, HZ-AM1, was also suitable for propagation of IsCLO and kept a steady state with bacterial growth. Using IsCLO-infected AeAl-2, antibiotics effective against the bacteria included ampicillin, chloramphenicol, penicillin-G, rifampicin, and tetracycline. These antibiotics will be useful for eliminating CLO from host arthropods, which is necessary for in vivo studies of the intracellular facultative symbiotes.