Autoclave times

Alec Gallagher alec at colindal.globalnet.co.uk
Sat Sep 5 16:06:57 EST 1998

At least one leading manufacturer in the UK bases its 121 C for 15 minutes
sterilisation temperature/time on the parameters necessary to sterilise one
litre of medium, presumably in a conical flask or large bottle.

There are so many variables - the autoclave, the shape and size of vessel,
how heavily the autoclave is loaded, how quickly the autoclave heats up,
even the viscosity of the medium.  Given all this, I think the best way to
determine whether a medium has been treated adequately is to see whether it
does what it is supposed to do.  So, check for:

1) Sterility - incubate the uninoculated medium and check for growth - if
none appears, the medium has at least been sterilised.

2) Productivity - inoculate the medium with an organism which the medium
should support - if it doesn't, chances are you've overcooked it.

3) Selectivity - inoculate the medium with an organism which the medium
should inhibit - if it doesn't, overcooking is pretty much confirmed.

The last two are of course dependent on the fact that all other things
(addition of other ingredients post-autoclaving, incubation temperature etc
etc) are correct.  And of course selectivity can be something of a problem
with non-selective media.  But you get the idea.



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