What Is the foam-like substance in my agar?

[manifestomiku]

I have a science fair project in which I finished to do my procedure.

I am testing which hand sanitizer kills more bacteria.
I used prevail ( Duane Reade Brand) Lemon scent and Purell with aloe.
The experiment involves swabbing of both hands and waiting for bacteria to grow (approximately 24-48 hourss) in each agar plate,
and later placing 5 ml of the hand sanitizer ( by brand in the correct agar) In agar A i placed purell, In Agar B i placed prevail.

After 2 days (after I placed the hand sanitizer) Agar B with prevail has turned into a foam like mousse.
It does not look like mold for it isn't sticking in the agar plate.

[donnahardy2]

Hi,

I apologize for the delay in responding to your inquiry. This is a very interesting project.

Bacteria will generally have a distinctive appearance and generally do not look like foam, and the shape and size of the colonies changes over time.

http://www.google.com/#hl=en&biw=973&bi ... 5d937ac077

So, if your foam has not changed in appearance, then it is probably not bacterial growth and the Prevail hand sanitizer was effective. What were your results with the other two products? Did you run any controls with no sanitizer and one with no hands?


Donna Hardy

[manifestomiku]

I apologize for the really late reply (school work and such).

I have 2 trials done one with heat and one without heat

Trial 1 with heat constant temp of 90

Number of Visual Colonies
Day A-Purell B-Prevail Control
1 0 0 0
2 4 0 0
3 6 3 4
4 6 4 Lawn Hand Sanitizer Applied
5 6 Foam Lawn

I have found out that the organisms I have counted were actually growing mold
Due to the heat source.

Trial 2 without light constant temp of 65
Day A-Purell B-Prevail Control
1 0 0 0
2 0 0 0
3 1 0 3
4 13 small 0 10
5 17 1 21 Hand Sanitizer Applied
6 12 lawn 26

Due to the slow growth I extended my time period of observation by adding 1 more day.

[donnahardy2]

Hi,

Thanks for posting your data. I think I understand what happened. One way to do an experiment like this is to apply the hand sanitizer at the beginning of the incubation period, and compare results with another sample that has not been exposed to the hand sanitizer. You would expect more colonies to grow on the sample that has not been exposed to hand sanitizer, and the difference in the number of colonies would be your result. Since you incubated your plates for 5 days and then applied the hand sanitizer, there’s not really a good way to measure results.

If you have time to repeat the experiment, please do include the independent variable at the beginning of the incubation time and compare results. If you don’t have time to repeat the experiment, then you should proceed because you do have some very interesting data; you will have a more interesting conclusion and discussion section with your current results.

Here is a Science Buddies project that shows how to measure the effectiveness of anti-bacterial agents by measuring zones of inhibition. This would be another way to do this experiment:

https://www.sciencebuddies.org/science- ... p014.shtml

Why do you think it took so long for colonies to appear on your plates? Why did colonies continue to appear on the plates after you applied the hand sanitizer? Your results raise some interesting questions.

I hope this helps.


Donna Hardy

[manifestomiku]

I think it the slow growth was due to the temperature, and the reason they keep on growing is because of the nutrients provided by the agar.