Science Buddies: "Ask an Expert"

My science fair consists of testing the effects of Lactobacillus Acidophilus on Bacillus Cereus, but I will need to kill off the Lactobacillus Acidophilus at the end of the experiment so that I will be able to count just the Bacillus Cereus. I am not quite sure how to achieve this and I think there may be a media out there that may get rid of one but not the other, even though they are both gram-positive. If someone could assist me in finding a method, I would appreciate it. Thank you.

Hi,

This is a very unique and interesting idea for the science project. Here is some information that should help:

Lactobacillus and Bacillus species are very different even though they are both Gram-positive. I believe you should be able to find an antibiotic to use that will inhibit the Lactobacillus, but allow the Bacillus to survive.

Here is a reference that lists the general antibiotic sensitivity for Lactobacillus acidophilus:

http://www.ncbi.nlm.nih.gov/pubmed/8543330

Here is a paper that lists the antibiotic sensitivity for Bacillus species. The results for several isolates of B. cereus are included on Table 3 in this paper.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC497625/

You may need to do additional searches for “antibiotic resistance of lactobacillus” and “antibiotic resistance of Bacillus,” to find more data. You will need to check to find out what antibiotics you can purchase.

So, what antibiotics would be suitable for your experiment?

How long will you be growing your cultures? If the Bacillus cereus is present as endospores at the end of the experiment, then you could use heat to kill the Lactobacillus.


Please post again if you have more questions.

Donna Hardy