uniform colony distribution

Paul N Hengen pnh at fcsparc6.ncifcrf.gov
Wed Dec 14 17:20:34 EST 1994


 In article <rapr-1312941438170001 at quadra800.pathology.pitt.edu>
 rapr at med.pitt.edu (Robert Preston) writes:

> A method that seems not to be widely known, but works very well and is easy
> to learn, and requires no beads or sticks (it does require sterile
> pipettes, though, OR sterile rims on your transformation sample tubes).
.
> Deposit the sample in the center of the plate, and then spin the plate
> (not too fast) while pushing the tip of the pipette slowly toward the far
> side of the plate....
.

Some time ago, I saw a demonstration of a mechanical device which rotates a
petri dish at a set speed and delivers a specific amount of inoculum from the
center of the plate to the outside edge, with less and less material delivered
as the stylus moves outward.  By counting the colonies on the furthest and most
dilute rings created, one can calculate the CFU/ml in the original culture.
I haven't seen one of these things in years and wonder if they are still around.

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