Indian spices vs Bacteria

[greyelephantlover]

Hello! I am in the 10th grade, and I needed some help on my science fair project.
So, I am going to test Indian spices on E. Coli. I will order the bacteria from Carolina Biological. My independent variables would be the type of spice, my dependent would be the effect on the bacteria, and I can have one petri dish with no spice as a control to compare the effect.
I want to use the disk diffusion assay to do my experiment, but I have heard that I have to dilute the spices first, and then soak them in the paper disks, and then place them in an inoculated petri dish. I need assistance on how exactly I have to dilute these spices. (use heat/no heat, how much water per amount of spice, etc) Also, do you think this experiment will work in your opinion?

I would really appreciate it if I could get some advise and help.

Thank You!!

[Saanya]

Hi!
Interesting idea! I can't say for sure if the experiment will "work," per say, but it definitely sound like a solid idea.

As for your method, I don't think a disk diffusion assay would be the best approach. The problem is that you'd need to put the same concentration (morality=moles of spice per liter of water) of spices in each of the disks, and there is not a very accurate way to measure the number of moles of a spice since it is not a pure molecule/compound.

I would suggest maybe getting multiple petri dishes (one per spice and a control one). You can maybe mix the same amount of spice into the agar of each petri dish and measure the amount of growth of the bacteria as compared with the control. Or for a more direct comparison, maybe you can place the spice on top of/mixed into only half of the agar in each petri dish and see the differences in where the E.coli prefers to grow.

Good luck!
Saanya

[greyelephantlover]

Thank You so much for the quick reply. So you are saying that I can't do the disk diffusion, but I can mix the spice in with the agar? Does this allow the spice to spread into the bacteria culture? Also, how would I compare the effect? Would I have to count the colonies?

[greyelephantlover]

Also, for whole spices, I would still have to melt/heat it? I'm sorry for all the questions. I'm just a little confused here.

[Saanya]

Hi!
No problem!
What the agar is is food for the bacteria to grow. By implementing in the spices, there might be a change in the number/placement of the E coli (maybe away from the spice, or just less E. coli in certain spices), especially if the spices are harmful or deterrents to the E.coli.
It's difficult to get a true quantitative answer to your experiment with just the number of colonies since some are bigger than others or hard to discern, but perhaps you can find the approximate total area occupied by the E. coli. Most colonies are circle-shaped, so it might be a lot of math, but you can approximate the total area occupied by using the circle area formula ((pi)r^2) for each colony of a petri dish and then adding the total area up for each dish.

Saanya

[Saanya]

Also, with whole spices, try grinding them into powder form through a blender so that you only have one independent variable- type of spice!

[greyelephantlover]

Thank You! So I get liquid agar and mix in the spices, and then pour it and let it harden?
I think I will have trouble counting the colonies, and I was really hoping if I could've done the disk diffusion, but I will try my best! Let's hope this experiment works!

[Saanya]

Hi,
Yes! Good luck! Don't be disheartened if you don't see the results you expect to- no matter what, you will learn something and will have something to talk about/present to others!

-Saanya