bubbles and agar plates

Frank O. Fackelmayer Frank at Fackelmayer.de
Wed Jul 18 02:34:26 EST 2001

John Rebers wrote:
> Occasionally I have problems with agar plates used for growing bacteria
> with small bubbles (2-3 mm in diameter) appearing between the plate and the
> agar medium. These are not on the surface of the plate or within the agar
> itself, but are air bubbles at the bottom of the plate between the medium
> and the agar. The bubbles are invisible at room temperature, but expand
> significantly when the plates are incubated at 37C. They are sometimes
> abundant enough to make it more difficult to distinguish colonies on the
> plate surface. Since they only show up some of the time, I suspect this has
> something to do with the way the plates are poured - the temperature of the
> medium, perhaps. Has anyone else seen these and figure out how to avoid them?

Hi John,
Bubbles between the platic plate and the agar are quite common. It is a
good idea to let the plates stand at room temperature after pouring for
at least 12h (we usually do it overnight). Anyway, bubbles are not a
real problem as they shrink to invisibilty when you chill the plates.
Put them into the cold room or fridge for a couple of hours if the
bubbles are too disturbing. 
To distinguish the bubbles from colonies, do not look directly through
the plates, but look at them from above, at an angle.


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