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Bigbad
Bigbad asks:
Q:

Germ Jungle Project Question

Why am I not seeing any bacteria growth on the agar in the petri dishes?  I purchased a petri dish set at a teacher's supply store which included a jar of powdered agar.  The instructions in the kit instructed me to mix the agar powder with boiling water, allow it to cool and then spread the agar in the petri dishes.  After which, the instructions were to begin swabbing the germ surfaces (e.g. cell phone, refrigerator handles, etc. and rub the swab onto the agar) and then seal the container.  I performed those steps, but am seeing no growth on the agar.  I tried another plan.  I didn't boil water and mix the agar powder, I just spread the powder in the petri dish and then followed the swabbing steps mentioned above.  Can anyone tell me where I may be going wrong?  Thanks!
In Topics: Science fair
> 60 days ago

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graham
graham writes:
The boiling of the water is to kill any bacteria which might exist in the petri dish, and to create a sterile environment in the dish, you do not want to skip that step.

The idea of agar is to give the bacteria the required glucose and nutrients to grow. It is possible that the agar you purchased is non-nutrient agar.

To grow the bacteria properly, place each Petri dish inside a zip lock bag (to prevent drying out and to control odors) and turn the plates upside down in a warm place. For many microorganisms, the ideal temperature for incubation is 32°C or 90°F. Bacterial growth should start to become visible in 2-3 days.

Perhaps the swab you're using is antibacterial? If you want to see if your agar dishes will work at all, try coughing into one and apply the same procedure.

Those are my ideas. Hope this helps!
> 60 days ago

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Bigbad
Bigbad writes:
Thanks a million, Graham!  I'm going to give it another shot.
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