Expert: Walter Hintz - 10/5/2008

Question
QUESTION: Hi, My daughter (Rebecca)  and I are working through an experiment testing out the "Five Second Rule".  We prepared our bacteria food as directed (1 cup distilled water, 1 boullion cube and 1 T gelatin)  It solidified just fine in the pertri dishes and we were able to do the swabs with no problem.  But then when we placed the dishes in our incubator (fish tank with desk lamp inside- keeping temperature between 98- 101 degrees F as best we could) the homemade bacteria food liquified and nothing grew in it - that we could make out.  Not to mention that each time we tired to observe it, we would just swirl around whatever had formed...  We did the identical thing with store bought agar - and we have observable growth - but my daughter really wants it to work with homemade food.  Were our proportions wrong?

ANSWER: Hi Rebecca; I cannot answer as to why the gel liquified unless ot got to hot.  If you try again try incubating at room temperature.  Growth is slower but bacteria will still grow.
 I am curious as to your results with the agar. What were your results

---------- FOLLOW-UP ----------

QUESTION: Well, we noticed that wet food (banana) grew bacteria more frequently than dry (graham cracker) - but the location was not as much a factor.  We checked our kitchen, the park sidewalk, park grass and the boys' park bathroom) Our home kitchen grew bacteria more than the park sidewalk.  My mother is horrified.  (And one sample taken in the boys' bathroom at the park grew nothing at all.)  What does that say about our kitchen?!?  We think that the "Five Second Rule" might be a sort of "Take your Chances" kind of thing.  We think we will try this experiment again with no incubator.  How often should we record results?  And will we risk having mold grow as well?  Finally, does the color of the growth say something about the type of becteria?  We noticed cloudy whitish growth mostly but we also have a couple of very yellow spots in two of the dishes.  Thank you so much for you expert help!

Answer
 Without incuabtion the growth will slower and maximum growth should occur in about a day and a half.  Some bacteria colonies have color. The yellow colonies are probably a bacterium called Sarcina lutea.  The cloudy growth is most likely a Bacillus species which is just about everywhere.  The 5 second rule is nonsense.  The food is not sterile and is already contaminated with harmless germs. Any bacteria picked up from the ground is probably no different then what is already in your mouth. I would expect that a kitchen would have more bacteria than a sidewalk. I don't know about the boys bathroom.  There are a lot of factors that could account for that. maybe it had just been cleaned
Did you use controls. That is did you see what was on the food before you put it on the ground