Killing Lactobacillus acidophilus without killing E. Coli?

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Killing Lactobacillus acidophilus without killing E. Coli?

Postby KarenL » Mon Oct 29, 2012 9:11 am

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.
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Occupation: Student: 12th grade
Project Question: To topic of my science project is Medical Science. I have not yet decided what to specialize my project.
Project Due Date: 10/30/2012
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Re: Killing Lactobacillus acidophilus without killing E. Col

Postby donnahardy2 » Tue Oct 30, 2012 4:49 pm

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.

Here is a recipe for EMB agar:

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

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

Please post again if you have any other questions.

Donna Hardy
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