Springer Online Journal Archives 1860-2000
Abstract Eimeria tenella sporozoites exposed to 100, 70, 60 and 50 μg salinomycin sodium (SAL)/ml medium 199 at 41° C and then stained with propidium iodide/fluorescein diacetate were analysed by means of flow cytometry (FCM). After 20 min exposure, they showed dose-dependent alterations in their size and shape, i.e. ballooning of most cells, and enhanced intracellular esterase activity as compared with untreated controls. After longer exposure periods (40 and 70 min), inflated cells gradually changed into shrivelled or crumpled, nonviable ones, thereby showing a gradual decrease in esterase activity and a gradual loss of membrane integrity (RFA+). As compared with untreated controls, sporozoites treated with 10 μg SAL/ml showed negligible RFA+ values (0.4%–2%), whereas those exposed to 1 and 0.1 μg SAL/ml and to the solvent dimethylsulfoxide (DMSO, 1%) did not, even after 70 min exposure. Slight to severe structural changes manifesting as an extremely wavy surface (1 μg SAL/ml), vacuolization of the cytoplasm, distension or destruction of the mitochondrion and rupture of cell membranes (10 μg SAL/ml) were seen not only at higher SAL concentrations but also (rarely) at lower ones. The ability of sporozoites to invade primary chick-kidney cells was significantly inhibited by 70, 60 and 50 μg SAL/ml. In general, there were close relationships between findings obtained using FCM, electron microscopy and an invasion-inhibition test. The results indicate that FCM is a reliable and sensitive technique for characterizing the parasiticidal effects on and the possible mode of action of drugs in free coccidian sporozoites.
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