4741
( 1986 ) method of separation of Cryptosporidium spp . oocysts from feces by using a percoll discontinuous density gradient appeared a method of choice for obtaining large numbers of oocysts of C . parvum free of fecal contamination .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None