Quote:
Originally Posted by NatalieS
Ray, you make a good point about the treatment of the flasks after removing them from the microwave. Re-reading Mxptrsn's post I missed the fact that he'd closed the flasks straight after putting them into the plastic bag sprayed with bleach. I used the same procedure (except I used sodium hypochlorite instead of bleach) and got zero contamination. However, I left my flasks slightly open while cooling in the sealed bag which would've caused the sodium hypochlorite to be sucked into them.
Some of the flasks I sowed the next day, some a few weeks later - zero contamination even in the later ones, so I'm confident the microwave method works.
Edit: Thinking about it a little more, I still think it's just down to heating the medium for long enough. Technically, the super-heated steam from the medium should sterilise the microwave and the atmosphere in the flasks.
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When I think about what I'd done with regard to the procedure I went through, I think using pp containers may be the source of the problem. You know, when I transferred them from microwave to the pre-sprayed plastic bags (I sealed them when they cooled down a little bit in the plastic bags), the contaminants could have got in through the air first. So, that could be the source. Now I've tried to use baby food jars and pressure cooker, the contamination rate is significantly lesser than using pp containers.
I have also tried using baking oven, I'm still waiting to see if there's any sign of contamination. If it works, i'd say that it could be one of my sterilization alternatives.
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