Student Post-Experimental Advice

books at books at
Mon Feb 7 10:02:14 EST 1994

My sons fourth grade science project is to test which sandwich spread will
grow bacteria the best and we need some scientific advice.

Materials and Methods
The experiment is spread mustard, ketchup, mayo, jelly, peanut butter, butter,
horseradish on a separate bread slice. The control is a bread slice without a
spread. The experiment was done in triplicate one set was left at room
temperature exposed to the air, one set was place in a ziploc then left at room
temperature, and one set was placed in a plastic container then refrigerated.

After four days we visually observed no bacteria, no fungus, nothing!

We then sampled each spread by plated on LB agar plates. Only peanut
and peanut butter(bag) developed bacterial colonies. No colonies were detected
for butter or mayo? We expected positive results for butter and mayo.

The question is what bacteriological test could we do to better detect
bacterial growth?

Any advice would be welcomed.
Thanks DPSMITH internet:smith_dennis_p at

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