in the Excystation Process of Eimeria tenella Oocysts and Sporocysts

ABSTRACT The role of pancreatic proteolytic enzymes in the excystation process of Eimeria tenella oocysts and sporocysts was studied in vitro. Intact sporulated oocysts were preincubated in phosphate buffer, NaCl 0.9 % (PBS) added with 0.5 % chicken bile extract in a 5 % C02 atmosphere for 30 minutes prior to exposure to either 0.25 % (w/v) chicken trypsin, chymotrypsin, pancreatic elastase, or a 1 % (w/v) crude extract of unsporulated and sporulated oocysts of E. tenella (Expt.1). No excystation was observed under these conditions. Sporocysts were also incubated under the same conditions without pretreatment in C02. Excystation was observed for sporocysts incubated with either trypsin, chymotrypsin or pancreatic elastase, the best percentage of excystation being recorded for the latter after 5 hours (Expt. 2). Crude extracts of E. tenella oocysts failed to bring about excystation of sporocysts at any time. In experiment 3, sporocysts were incubated with either trypsin, chymotrypsin, or pancreatic elastase alone, any combinations of 2 of these enzymes or with all 3 enzymes. The best percentage of excystation was observed after 5 hours with sporocysts incubated with trypsin and chymotrypsin (99%). The other combinations of 2 enzymes gave also comparable results. Sporocysts incubated in the presence of the 3 enzymes excysted similarly well, although a significantly lower percentage (P<0.05) after 5 hours was recorded when compared to that in sporocysts incubate