My 6th graders are studying fungi. We have innoculated
various media with spores from mold grown on bread, cheese, fruits,
etc. Did I have to altoclave the growing media before it was
innoculated? We are using 4 growing mediums.... mashed potatoes with
water, mashed bananas with water, tomato sauce, and a yeast solution
(yeast and water, no sugar) covered with moistened bread.
We have fielded this question before. Check the NEWTON BBS archives.
Sterilizing the media is always a good technique, but it seems that your
project does not require it. My feeling is completely different. If you
are not qualified to identify the numerous hazardous and extremely
hazardous fungi and bacteria that may be growing on your plates, you should
not perform this activity, in my opinion, in a classroom setting. Take the
precautions of not getting your students sick and sterilize everything when
you are done.
If you are qualified, I apologize, but others will be looking at this note
when it is posted.
If your media aren't autoclaved you may get some contamination with bacteria.
Most bacteria are inhibited by acidic conditions however, so the tomato
based media may be less hospitable to bacteria. Let me know how your
experiment goes-I'd be intersted to know your results.
Basically, autoclaving would sterilize the media prior to inoculation. Not
autoclaving permits the growth of other bacteria and fungi already present
in the media.
If you only wanted one kind of spore per experiment and controls without
any fungi, then autoclaving would have been useful.
Anthony R. Brach, Ph.D.
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Update: June 2012