human/bacterial DNA ratio?

tivol at tivol at
Tue Aug 16 13:48:30 EST 1994

Derek Ellison asks about the ratio of DNAs in stool samples.
	I have heard that human stool samples consist of about 50% E. coli
cells (mostly dead).  I wouldn't know how to estimate the surviving fraction
of the original DNA, but it seems that rather a lot would be there.  Other
DNAs from undigested cells in food might also be there to complicate the
situation even further.  The only human DNA I would expect is from sluffed-
off intestinal epithelia.  I would guess that the intestinal tract would be
very efficient at absorbing bases and small DNA fragments.  How all this con-
tributes to the ratio is hard to predict.  Perhaps a CG vs AT ratio would be
useful--especially if the ratio is very different for humans vs E. coli.
				Bill Tivol

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