Analysis of coccidian oocyst populations by means of flow cytometry

Flow cytometry was employed as a tool to analyze and characterize batches of oocysts from laboratory and field isolates of Eimeria spp. from chickens and to propagate sub-populations of batches of oocysts. Oocyst batches were cleaned of debris by a combination of salt flotation, washing and treatment with dilute sodium hypochlorite (1.5% aqueous). Oocyst size and shape were registered by forward-angle light scatter with the argon laser excitation set at 488 nm at 300 mW. Sub-populations of oocysts were collected by map gating and used for microscopy or for propagation. The profile of particle size was characteristic for each species. Propagation of sub-populations of oocysts of specified sizes resulted in cultures of coccidia that were pure species or nearly pure species. The small size of E. mitis caused difficulty in separation from the remaining fine debris. This technique was useful for studying the mixed isolates by bit-map gating had the same limitations as micromanipulation because of the overlapping size of Eimeria spp. Characterization is further limited by the lack of suitable size/shape standards for flow cytometry.