Eimeria tenella: screening of chemotherapeutic compounds in cell cultures

Preliminary studies indicate that screening for anticoccidial activity is feasible in a cell culture system. Ten compounds shown to be active in vivo were tested against a field strain of Eimeria tenella (from the cecum of the domestic chicken) cultivated in primary embryonic chick kidney cells grown in Leighton tubes. The drugs, added to the culture nutrient containing the sporozoite inoculum, were prepared at levels of 100, 10, and 1 μg/ml. Because cytotoxity occurred with dianemycin, monensin, nigericin, antibiotic X-206, and to a lesser extent with antibiotic A-204, the 100 μg/ml suspensions of these insoluble drugs were filtered through a millipore filter (0.22 μm), thereby reducing not only cytotoxicity but the final concentration as well. Amprolium was readily soluble; buquinolate, decoquinate, glycarbylamide, and nicarbazin were largely insoluble and except for nicarbazin at the 100-μg level, did not appear to affect the cells adversely. In addition, two compounds known to be inactive against E. tenella in vivo were tested also; both were soluble and neither was cytotoxic.Cultures were fixed and stained after 72 hr of incubation when many mature first generation and early second generation schizonts appeared in control preparations, and at 96 hr when mature second generation stages were present.The results showed that all of the ten compounds active in vivo were also active in vitro within a 72-hr period of development, while neither of the two inactive materials was effective. Activity was manifested by an easily detected reduction or elimination of schizogony when compared with untreated controls, the absence of any second generation development, or by the appearance of abnormal sporozoites, trophozoites, or immature schizonts.In vitro screening for anticoccidial activity appears to be an effective, rapid method which requires only microgram quantities of the materials to be tested.