Effect of the microbiota on the development of the parasite Eimeria tenella
Résumé
Coccidiosis is caused by the parasite Eimeria, the first parasite in poultry farms. E. tenella, the most virulent specie colonize the caeca rich in bacteria. Our objective was to study the impact of intestinal microbiota on E. tenella infection. An original model of germ-free and conventional broilers was developed. While using the same dose of E. tenella inoculum, germ-free chickens excrete 4000 fold less oocysts than conventional chickens 6 days post-infection. This lower parasite load in caecal tissues is measurable as soon as 2 days post infection. Several biological processes in the parasite cycle may explain this result (excystation, invasion, development, …). As the excystation is the first step of the parasite cycle, in vitro capacity of excystation of the parasite using intestinal contents and biles of chickens was studied. When using duodenal contents and biles from germ-free chickens, the excystation rate of sporozoites was higher in contrast to those from conventional chickens. To shunt the excystation step in vivo, chickens were infected with sporozoites by cloacal inoculation. Parasite invasion after 24h infection was similar between germ-free and conventional chickens. However, after 7 days of infection, there was still less parasite excretion and parasite tissue load in germ-free chicken compared to conventional chicken (500 fold) suggesting that the microbiota and its metabolites may play an important role on parasite replication. We also studied the development stages of the parasite by using specific gene of different parasite stages. A delay of schizonte and gamete specific gene expression was observed in caeca of germ-free chicken compared to conventional chickens. Overall, these data suggest that the microbiota and its metabolites may play an indirect role on bile content and subsequently on the excystation rate and, also on the parasite development. Consequently, modulation of microbiota composition could influence coccidiosis severity.