Re: Tryptone broth test for sterility check


<msalguod@xxxxxxxxx> wrote in message
news:1143208044.677180.69360@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Our first test had alot of what looked like white sediment on the
bottom of the sample and the smple was cloudy. I wasn't sure if this
was growth or some sort of precipitation.
I set another batch and I purposely contaminated some and put in some
plain DI water. Still they all looked the same.

The simplest test is to stick it under a microscope and see if there's any
bacteria or yeasts in there.
Also, streak a bit onto a tryptone or peptone agar plate and see if anything
grows.

I checked the autoclave settings and saw that they had it set for the
mininum 15 minute hold at 122° C.

How big is the autoclave? With little pressure cookers, it's not a problem,
but if big autoclaves are not packed correctly, with space left for air
flow, the centre of the load does not reach the correct temperature. Ours
always have a thermoprobe in a bottle in the heart of the load. Has your
autoclave been serviced and validated regularly? Ours are done annually.
Try including a bottle of a rich medium (such as tryptone broth or peptone
water) with your batch of dilution water. There is always the chance that
your samples are becoming infected after sterilization, when the tryptone
broth is added.
You dont say what volumes of dilution water you're using per run - we have
found that it's more convenient to filter sterilize low protein, low
particulate liquids if they're not used in huge amounts.
Lesley Robertson


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