Inhibition of the respiration of Eimeria tenella by quinolone coccidiostats

Abstract

The protozoan parasite Eimeria tenella respires vigorously during sporulation and excystation. Sporulation is initiated and sustained by the respiratory activities, and cannot take place under anaerobic conditions. Excystation is not necessarily associated with oxygen consumption and seems to be a passive process solely carried out by the host. Quinolone coccidiostats such as amquinate, buquinolate, methyl benzoquate and decoquinate are reversible inhibitors of E. tenella respiration and sporulation. The effective concentrations of the inhibitors for 50 per cent inhibition are 1 to 2 × 10 −5 M against respiration during sporulation and 3 × 10 −6 M against respiration during excystation. The respiration in sporulation and excystation of an amquinate-resistant E. tenella mutant is much less subject to inhibition by the quinolones. The results suggest the inhibition of coccidial respiration as the possible mechanism of anticoccidial activity of the quinolones. Some 2-hydroxynaphthoquinone coccidiostats are also strong inhibitors of E. tenella respiration, but they are equally effective against the wild type and the amquinate-resistant mutant.