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Fungus growing on agar plates. contamination??

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Postby michimichi » Wed Jan 25, 2012 8:24 am

the source of the contamination would be from air since you said you didnt pour it under the hood.
It might also be from the plate or the media which was not properly sterilized.
Its okay not to wear gloves but be sure to disinfect you hands and do proper aseptic technique.
..and also, dont talk when pouring agar...if you cant help it, use mask instead.
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Postby JorgeLobo » Wed Jan 25, 2012 1:31 pm

Don't worry about your hands being the source (you can't "sterilize" them and fungi are not flora you'd expect) and it's doubtful you're seeing actinomycetes. Think skeptic has the right idea. Unless your sterilization is inadequate (is your autoclave validated?) it may be more a function of air contaminants in room or frig finding theirinto your plates. What do you do with plates after pouring and solidification? Try replacing poured plates in the plastic sleeves or even in stainless steel canisters
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Postby michimichi » Wed Jan 25, 2012 2:08 pm

another thing is ,how did you store the unused plates with agar?
put it in a zip lock and store it (upside down) on the fridge (do not freeze) for future use.
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Postby tom1193 » Mon Jul 02, 2012 5:50 am

I always pour from a beaker covered with sterilized foil, with only the mouth uncovered to pour. Do this right after it is done autoclaving. Doing it next to a flame is not enough to keep contamination out of the agar. I also flame the mouth before every pour. The contamination usually comes when your pouring; your plates shouldn't become contaminated after a few days if you properly poured.
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Postby citroenboom » Tue Jul 17, 2012 6:59 am

In my lab the cold room is a nice source of some black fungi (we need to clean). Only carefully closed bags are good enough to keep it out. So I think it is air and water droplets in in the air.
Just be carefull when pouring and storing. Pouring next to the flame and storing upside down in a bag in a clean room or fridge (works for me). The bag is mainly to prevent it to dry out.
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Postby Atropa » Fri Aug 03, 2012 4:48 am

If you don't want contamination, then you need to control for it. You should be using a sterile technique for everything. And your plates should never be open and exposed to air longer than it takes to pour the agar or inoculate your medium with a sample...
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