Cryptosporidium parvum: oocysts purification using potassium bromide discontinuous gradient.

Cryptosporidium parvum oocysts were purified using a discontinuous potassium bromide density gradient, composed by three solutions of 6, 16 and 28% (w/v) KBr in Tris-EDTA buffer. Fecal samples containing oocysts were washed to diminish interfering lipids and applied to the gradient. After centrifugation, oocysts can be easily aspirated from a clear band, diluted and washed by centrifugation in phosphate buffer to remove residual KBr. This method allows the purification of large amounts of highly purified C. parvum oocysts, using low cost reagents and a standard table-top centrifuge.