Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva

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VegaYOLO100
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Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva

Post by VegaYOLO100 »

Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva


Attachments.doc
1: Toilet Seat 12/13/20
2: Garbage Disposal 12/13/20
3: Human Mouth 12/13/20
4: Toilet Seat 12/18/20
5: Garbage Disposal 12/18/20
6: Human Mouth 12/18/20

antibacterial 1: 91% Isopropl Alcohol
antibacterial 2: H2O2
antibacterial 3: Vinegar
antibacterial 4: Listerine
antibacterial 5: Distilled Water (Control)
antibacterial 6: Organic Honey

Experiment completed on 12/11/20

Questions:
I don't understand what is going on with these set of dishes: "3: Human Mouth 12/13/20" in Attachments.doc. 2 days after the experiment, there seems to be something growing around the honey [6: Organic Honey]. What could that be? Also, compared to "2: Garbage Disposal 12/13/20" and "1: Toilet Seat 12/13/20" there seems to be no growth except for some white dots in sections "6: Organic Honey"; "5: Distilled Water (Control)" and "3: Vinegar". What could that be?

I also don't understand what is going on with these set of dishes: "4: Human Mouth 12/18/20" in Attachments.doc. 7 days after the experiment. What are those white dots and blobs and why are they concentrated around "6: Organic Honey" & "5: Distilled Water (Control)"?

Thank you so much for any assistance you can give me.

Attachments(1).PDF
Student PDF
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cmpayne
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Re: Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva

Post by cmpayne »

Hi VegaYOLO100,

This is a great experiment, and it looks like you have been very thorough in setting it up! As for the white dots and blobs that appear around your control (distilled water) and organic honey, these are your bacterial colonies. In your toilet seat and garbage disposal dishes, you see the colonies have flourished except around the perimeter of a few of your antibacterial substances.

In the case where you sample the human mouth, you see many fewer colonies have formed. This could be due to a couple of things. The simplest explanation is that the concentration of bacteria in the human mouth is much lower than that of the toilet seat and garbage disposal samples. Alternatively, the human mouth might have a type of bacteria that grows better at elevated temperatures (~37 deg. C). Either way, you only see growth around the honey and water, which is related to the antibacterial properties of those two substances. In other words, honey and distilled water don't do much to prevent bacteria from growing.

Hope this helps you make sense of your results!

Best Regards,
Dr. Christina Payne
VegaYOLO100
Posts: 2
Joined: Fri Dec 18, 2020 2:06 pm
Occupation: Student

Re: Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva

Post by VegaYOLO100 »

Dr. Christina Payne,

"In the case where you sample the human mouth, you see many fewer colonies have formed. This could be due to a couple of things. The simplest explanation is that the concentration of bacteria in the human mouth is much lower than that of the toilet seat and garbage disposal samples. Alternatively, the human mouth might have a type of bacteria that grows better at elevated temperatures (~37 deg. C). Either way, you only see growth around the honey and water, which is related to the antibacterial properties of those two substances. In other words, honey and distilled water don't do much to prevent bacteria from growing. "

Since the growths are only around the honey and distilled water and not in any other parts of the dish, are honey and distilled wate a food source for the human mouth bacteria? Is it possible that the agar was not enough of a food source and the honey and distilled water provided something that bacteria needed to grow? Could it be dangerous? botulism from the honey? I wish I had references to look this information up.

Thank you
cmpayne
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Re: Homeschool Science Project: kirby bauer assay issue with honey vs Human saliva

Post by cmpayne »

Hi VegaYOLO100,
Since the growths are only around the honey and distilled water and not in any other parts of the dish, are honey and distilled wate a food source for the human mouth bacteria? Is it possible that the agar was not enough of a food source and the honey and distilled water provided something that bacteria needed to grow? Could it be dangerous? botulism from the honey? I wish I had references to look this information up.
I think the explanation is neither that the honey and distilled water provided something that the bacteria needed to grow nor that the agar nutrients were insufficient. Rather, I think it is that honey and distilled water did not limit bacterial growth. And since they did not prevent the bacteria from growing, they do not make good disinfectants. The other antibacterials, such as peroxide and alcohol, are rather effective at limiting bacterial growth, which is why you did not see bacteria growing around these solutions.

You can find information on bacterial growth processes in microbiology textbooks or online resources. Here are a couple of links to some introductory microbiology concepts:
https://www.sciencebuddies.org/science- ... gar-plates
https://milnepublishing.geneseo.edu/sun ... e-methods/
https://open.oregonstate.education/gene ... robiology/
https://open.oregonstate.education/gene ... al-growth/
https://microbiologysociety.org/why-mic ... -dish.html
https://royalsocietypublishing.org/doi/ ... .1968.0063

Dr. Payne
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