I've been trying to extract Cryptosporidium DNA from faecal samples of human patients, sheep and cattle for some time now, and I can't get any DNA out of it. Since the staines slide of the these samples were positive.

My samples stored in 2,5% Potassium dichromate. I am using DNA stool kit from Favorgen and tried another kit from MoBio and Genomic aid, according to their protocol, but seems like it doesn't work that well for me. I tried various methods, including modified incubation time (according to some literature this works), do the beating for longer than suggested, still didn't work. Added an additional 95°C heating, still didn't work either. I tried to resuspended in water and filtered and washed through a mesh, still didn’t work too. The nanodrop shows good result. I assume that there was no target DNA in the extractions.

Any suggestions on successful methods for extracting Cryptosporidium DNA directly from faeces?