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In vitro antiparasitic effects of carob, grape and sainfoin extracts on rabbit Eimeria oocysts sporulation and excystation
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International audience. Coccidiosis caused by Eimeria species is a common, occasionally severe infection causing economic losses in the rabbit industry. The potential anticoccidial effect of tannin-containing resources fed in rabbits has been previously reported in vivo. However, the mode of action remains unknown. During this study, we investigated in vitro the anticoccidial effect of tannin-containing plant extracts by targeting two developmental phases of Eimeria life cycle: based on 1) an oocysts sporulation assay (OSA), 2) a sporozoites excystation assay (SEA). For this purpose, Eimeria oocysts of different species were harvested from naturally infected rabbits. Overall, 6 extracts of 3 plants (carob (Ceratonia siliqua) pods, grapes (Vitis vinifera) (skins and stems) and sainfoin pellets (Onobrychis viciifolia, var. Perly, harvested on 3 occasions) were prepared in PBS and tested at 0 to 1200 μg/ml for both OSA and SEA. For the OSA, freshly harvested oocysts were incubated with the extracts for 4 days at 26°C in order to enable sporulation. The sporulation rate reached 95% in all cases showing no significant effect of extracts. For SEA, oocysts were left to sporulate up to 98% before adding extracts. Solution was suspended first for 20h at 39°C in 20% CO2 with cysteine and NaHCO3, then 4h more with an excystation solution (0.4% trypsin/HBSS and 40% rabbit bile/PBS). Thereafter, excystation progress was checked every 4 hours until excystation rate reached at least 85% in controls. After 4 hours, grapes extracts inhibited oocyst excystation from - 53% (150 μg/ml) to - 85% (1200 μg/ml) (p<0.001). Carob extract used at 1200 μg/ml reached an excystation of 37%. Sainfoin effect varied depending on the harvest cut and year, with excystation rate ranging between 60 to 93% (lower excystation rate for a third-cut). These results suggest some disturbing effects of tannin-containing plants extracts on the coccidial excystation process.
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