Science Buddies: "Ask an Expert"

Hello, I am conducting an experiment dealing with bacterial resistance to naturally occurring antimicrobes, and one of the parts of the experiment involves culturing bacteria resistant to tannins (PAC) and I am unsure how exactly to do that. Help appreciated.

Hello,

This is an interesting project. What will be your source of tannins? Once you've determined your source you will need supplies for culturing bacteria. You can find these via a simple Google search (use words like bacteria and growth or kit) and I believe they can be purchased on Amazon.com. These kits will be composed of petri dishes, growth media (usually a generic growth media will be fine for E. coli), and agar(a jello like substance made from seaweed that acts to bind all other ingredients). You can then test the grown of E. coli in the presence of various concentrations of your tannin. Be sure to include a negative control (no tannins). Depending on the size of your kit, you should test 3-5 concentrations of tannins ranging from very dilute to very concentrated.

I hope this helps.

-Dave

Thank you!
Actually, I would like to know if it is possible to buy e.coli resistant to tannins and how long it takes the e.coli to become resistant to tannins, and then test a specific organic solution on the resistant bacteria... is it possible to get such bacteria?

Syntax,
I am not aware of any commercially available E. coli strains that are tannin resistant, but it would be fairly straightforward to develop one. You just start growing E. coli cells on an agarose plate (as described above) with a very low level of tannins. Take the colonies that grow and move them to a new plate with a higher concentration of tannins, then move those colonies, etc. until you have developed strains that are resistant to high levels of tannins. It should not take more than 3-4 transfers, which will take you about a week.

Thank you very much!

How do I transfer the colonies from plate to plate? Should I find a laboratory setting to do this experiment, or could it be done in a normal setting?

Hi,

Yes, since you might be working with unknown bacteria for this project, then you should try to find a microbiology lab to work in. It will make it a lot easier to do the experiments. If you used a sample from a high tannic acid environment and inoculated plates containing low to high concentrations of tannic acid, you would select for tannic acid-tolerant bacteria. I think that would be the quickest way to find an isolate.

Here’s an article that describes selection of tannic acid-resistant mutants of Saccharomyces cerevisiae that had been exposed to ethidium bromide. This would be another way to do your experiment:

http://www.ncbi.nlm.nih.gov/pubmed/11358167


Donna Hardy