Spiking Water with Bacteria

[deleted-572238]

I am doing an independent project on the efficiency of water filters, and I am hoping to spike water with bacteria and measure the levels before and after filtration. I am having a lot of trouble finding a good way to spike filtered water with the e.coli i have cultured on agar plates, I want to have 1 L of water with the bacteria in it to filter.

Anything on this subject would be super helpful!
Thank you in advance

[SciB]

Hi Leah,

I couldn't tell from your question what kind of trouble you were having. Are you putting a drop of the water before and after filtering onto a nutrient agar plate, incubating it for a day or so and counting colonies? If that is the case then you don't need to add a lot of bacteria to the water--just enough to be able to see colonies on the agar. Are you using distilled water? You want to be sure that you don't use chlorinated city water which could kill the E coli.

Please post again with more information and I will try to help you.

Sybee

[deleted-572238]

Thank you! I really was just struggling trying to find an efficient method to spike the water, I wasn't sure if you needed multiple colonies to have a large enough quantity of bacteria to filter out. I have three different filters, and am filtering one liter of water through each one. Is adding one colony of the bacteria to each liter of distilled water efficient, and to keep it equal for an experiment?
Thanks again!
-Leah

[SciB]

Hi Leah,

I'll try to answer your questions. The E coli culture you receive from the company (Carolina Biological, probably) contains billions of bacteria and each ONE can produce ONE colony. In order to get an accurate count of bacterial colonies, however, you need to have a certain minimum number growing on the agar plate--about 200. Too few colonies and the count is not statistically accurate. Too many and it becomes very difficult to count individual colonies.

It depends on how much culture you have, but if you have a couple of milliliters (mL) I would add 0.1 mL to one liter of distilled water. I will assume that a mL of your E coli culture contains 10 million live bacteria so 0.1 mL would contain 1 million cells. If you add that to one liter of water and filter it, and then put 0.1 mL of the filtrate onto the agar, you should get about the right number of colonies per plate.

If you have time, do this test first. Add 0.1 mL of E coli culture to 1 liter of water, mix it well and then remove 0.1 ml and spread it on a nutrient agar plate and incubate the plate at about 80 F for 24 hours. You should see 100-500 colonies on the plate if your culture is still viable. If not then you may need to get a fresh culture or add more than 0.1 mL to the water.

Let me know if you have more questions.

Sybee