Colonies not growing

[Jill]

Hi There,
I am trying to do the experiment How well do disinfectants work. I used ham as suggested in the experiment and used various disinfectants and water as the control. I swiped the petri dishes as instructed. I have read the question other people have submitted and responses. I initially place the petri dishes in a dark area that probably wasnt't warm enough. We moved the dishes to a different area and placed them under a warming light to bring the temperature up to around 90-95 degrees. I now have a lot of condensation and no growth after about 3 days. I realize the ham that I used also does have preservatives which may affect the bacteria growth. I have four agar plates left and was going to re-do the experiment. I have been storing the unused agar plates in the fridge. We were going to re-do the experiment with raw meat, but I read where you did not advise doing this, so I have held off re-doing the experiment. I am unsure at this time what food to use to make the experiment work. My science experiment with the written report is due by the Feb 20th. When I re-do the experiment should I keep the cutting board in a warm dark place. I am doing this experiment at home and I do not have an incubater, I was using a large apporx 3 gallon metal can with a light shining in to it with the agar plates inside, which kept the temp apporox. 90 -97 degrees. I am afraid of cooking the agar. Please help as I am unsure what I should do next.
Thanks
Jill

[MelissaB]

Jill,

In the other thread, Donna suggested using milk or raw vegetables. I think milk would be much more likely to give you results (since we all know that milk spoils easily!).

Keeping the cutting board in a warm, dark place is definitely a good idea--warm, dark places are good for growing bacteria.

As long as you have condensation, I would not worry about cooking the agar unless it is already dehydrated--which if you kept the covers on is probably not the case. Many bacteria grow best at approximately human body temperature, so I think that the temperature you have is fine...but you might consider moving the light away a bit so it does not get quite as warm.

I hope this helps, and good luck--don't get discouraged, remember that antibiotics were discovered many years ago when an experiment with agar didn't 'work' properly!