extracting very very dilute DNA

[Christine Wulff-Strobel]

I am looking for a way to extract DNA from single celled organisms which 
may be contaminating animal feed samples. Since the density of these 
organisms is similar to the feed particles themselves (when ground up and 
solubilized in water) simple centrifugation is not an option. Filtration 
has not been successful either because the feed clogs the filters.

     Does anyone out there have experience with or a reference for total 
DNA extraction/harvest from extremely dilute aqueous samples?

     Thanks in advance for you responses.