Experimental Development of Monensin Resistance in Eimeria meleagrimitis

The discovery of monensin-resistant field isolates of Eimeria meleagrimitis prompted an investigation of the ability of this parasite to develop monensin resistance in a laboratory selection experiment. A strain derived from a monensin-sensitive parent strain was intentionally selected for monensin resistance by propagation in monensin medicated turkeys in isolation, while the monensin-sensitive parent strain from which it was derived was cryogenically maintained as a genetic control. Comparison of the monensin sensitivity of the selected and parent strains demonstrated monensin resistance development in the selected strain by the fourth generation of selection. This is the first reported experimental development of monensin-resistant coccidia and suggests that unlike chicken coccidia, the turkey coccidium E. meleagrimitis possesses the ability to readily develop resistance to the polyether antibiotic anticoccidials under the appropriate conditions of drug exposure.