Microwave sterilization

Paul N Hengen pnh at ncifcrf.gov
Tue Dec 17 14:27:53 EST 1996

Bernard Murray (bernard at elsie.nci.nih.gov) wrote:

> From what I understand moisture is essential for the sterilisation
> process.  Another poster described a microwave based sterilisation
> unit that involved the generation of steam.  I don't think that
> simply microwaving dry glassware in the oven has any effect.

I don't think so either. To test it one could coat the inside of a bottle with
some bugs (oops! bacteria I mean) and zap it. Then pour a small amount of
tempered agar media into it and spin the bottle until it covered the inside.
Put it in the incubator overnight. I know someone who had to do this in order
to prove to his thesis committee that his bottles did not have any bacteria in
them!! I'm glad I didn't have these *doinks* on my exam board ;-)

> A one-off that I tried some time ago involved microwaving
> tubes of bacterial culture (an Ames/Salmonella strain) and then
> streaking them out.  I found that in this case that the culture did
> not have to get particularly hot before the solution contained no
> viable bacteria (it certainly did not require boiling).  These bugs
> are somewhat fragile so I wouldn't rely on this at home but it does
> show that sterilisation is possible.  You may thus be able to
> sterilise glassware if it is damp.

The correct sterilzation test I think is using a spore-forming bacteria like a
Gram+ Bacillus or something. In Pasteur's day (Paul says bowing his head) they
used a hay infusion that contained many such beasts. BTW, those swan-neck
flasks with beef/soy broth in them are STILL sterile after over 100 years!
You can see an original in the Pasteur Institute museum in Paris....way cool!
The pressure of an autoclave (15 psi, 20 min) is needed to burst the spores.

* Paul N. Hengen, Ph.D.                           /--------------------------/*
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