Science Buddies: "Ask an Expert"

Hello,
I am doing a research project about the inhibition of E.Coli O104:H4 by Lactobacillus acidophilus and noting if resistance to the L. acidophilus develops or not. To count the number of E.Coli present, I will need to use serial dilution. However, I only want to count the number of E.Coli and not the L. acidophilus, so I need a method to kill off the L. acidophilus only. I was wondering if there was any way to accomplish this and what media I could use to do so.

Thank you.

Hi Karen,

This is an interesting problem, but it is definitely possible. You can use a selective medium such as Eosin Methylene Blue agar. This medium inhibits the growth of Gram-positive bacteria such as lactobacillus and confirms the growth of lactose-fermenters such as E. coli. The Wikipedia article gives a good description of this growth medium along with a photograph of the typical metalllic green sheen seen with lactose fermenters.

http://en.wikipedia.org/wiki/Eosin_methylene_blue

Here is a recipe for EMB agar:

http://www.thelabrat.com/protocols/EMBmedia.shtml

Carolina Biologicals offers this agar in a number of formats. Enter "Eosin Methylene Blue Agar," in the search field:

http://www.carolina.com/

The Science Buddies website offers excellent information on microbiology techniques and troubleshooting. You will find this helpful if this is your first bacteriological investigation.

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

Please post again if you have any other questions.

Donna Hardy