Ask A Scientist Molecular Biology Archive

name         Travis
status       student
age          11

Question -   I blotted hamburg on agar. I soaked paper disks in water,
bleach,baby shampoo, ammonia, dish washing liquid, mouthwash, then placed
the soaked disks onto the agar. After 36 hours I measured around the disk
to see which solution was most effective in killing the bacteria.  It
seem to me that the dish liquid was most effective because there was a
larger pinkish area around it. The bleach area had yellow coloring around
it.  I am not sure which has killed the most bacteria?  The pinkish
result, or the yellow?  I am not sure which color the agar would change
once the bacteria is killed around it.
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If the bacteria are "alive", you should be able to see them growing on the agar.  The colors 
that the different chemicals turned are probably reactions with substances in the agar and 
not an indication that they kill bacteria better.  To determine which does a "better job", 
you must measure the size of the zone of inhibition, ie. the circle around the disk where 
no bacteria are growing.  Look on the list of ingredients in the dish soap for Triclosan, 
which is a good bacteria killer.  Bleach is also an excellent bacteria killer, but the taste 
and smell would not be good for cleaning dishes.
 
vanhoeck
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