Number of CFU in kefir??

How many probiotics are in, say a cup of kefir? The only information I can find is from http://www.healingcrow.com and they say "Furthermore, freshly made kefir can have an average microbial count as high as 10 billion cfu/ml. This includes a mixture of various bacteria and yeast strains. This means that a 500 ml glass of homemade kefir could contain as many as 5 trillion beneficial microorganisms or even more! "

Does anyone else have any other information on this?
Thanks!