plate vs. liquid discrepancies

Wed Jan 26 14:27:12 EST 1994

Dear W.X. and others,
I can at the moment think about two possible reasons why a strain is
more sensitive to a drug on plate than in liquid:
1. The osmolarity of the plate medium is higher than that of the liquid,
and it makes a difference (easy to test).
2. Is your liquid culture properly aerated? Albeit it seems unlikely,
even quite vigorously shaken cultures may be semi-anaerobic, especially
if you have a lot of medium in the flask. Plate cultures, however, have
as much air as they want. There is a chemical method how to determine
aeration rate in a given flask/shaker setup, but I am afraid that
I can't provide a reference or protocol (we did it in a lab course
in my first university year). However, I remember that the aeration
rate is moreless inversely proportional to the medium/free space
ratio, and that having 1/10 medium and 9/10 air in an Erlenmayer
is the best you can do if worried about aeration (further decreasing
the amount of culture does not help much).
I hope it helps


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