Science Buddies: "Ask an Expert"

Posted on behalf of student/family:
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I am helping my son with the following science project.
https://www.sciencebuddies.org/science- ... i-bacteria.

I have the following questions:
1. We are able to use a lab of a professor at a local university and utilize their incubator for this experiment. Would it be better to keep the plates in an incubator for 2-3 days than analyzing it after 24 hours?

2. I would like to know if we could make a variation in this project. We are wondering, in addition to testing the Silver nanoparticles ability to neutralize E coli, can we add probiotics / nanoprobiotics such as bifidobacterium/ lactobacillus to the colloidal solution and compare both? We will use two sets of five agar plates, and compare the zones of inhibition. Could you please suggest how we can do this? I will buy another freeze dried E coli from the website, in addition to the kit, so that we will have enough specimen to make the lawns on the plates.

I would greatly appreciate your thoughts.

Hi Amy,

I apologize for late reply on this thread, hopefully it can still be of help to the student. Here are my suggestions:

1. If the student has access to an incubator, it would be better to incubate the plates for no more than 24 hours. E. coli grow very rapidly at 37 degrees C (standard temperature of a bacteria incubator) and have the potential to overgrow or even dry out the plates if they are kept in the incubator too long. At room temperature (~25 degrees C), it will take a few days for the bacteria to grow, as indicated in the Experimental Procedure.

2. I think it would be possible to test the antimicrobial effects of probiotics like Lactobacillus or Bifidobacterium. The bacteria would have to also be ordered as freeze-dried stocks, reconstituted in the proper growth media, and then prepared same as the colloidal solutions. Lactobacilli grow best in MRS (De Man, Rogosa, Sharpe) media, while I usually grow Bifidobacterium in Brain Heart Infusion (BHI) media and under anaerobic conditions. Because bifidobacteria grow best anaerobically, it might be more feasible to work with lactobacilli here. The rest of the protocol will be the same as written, just the disks are soaked in probiotic cultures instead of the colloid solution.

Hope this helps!
-Brandi

Thank you so much for your reply.

Re: Lactobacillus. I could not find it on Home science tools website. I googled it and found many options. Would something like this work?
https://www.amazon.com/Freeze-Dried-Lac ... BGT66?th=1

In another thread on science buddies there is a description of how to reconstitute the Lactobacillus. I have few nutrient broth 2ml bottles. If I empty contents of the capsule in the broth and keep it for 24 hrs, would this be adequate for Lactobacillus to grow? This has 25 M CFU. Is this dose adequate or should I consider higher dose 50 M (2 capsules), 100 M (4 caps) etc.

Greatly appreciate your help!

Hi!

The probiotic capsules you linked from Amazon would be sufficient, you would just have to empty the capsule into the media you want to cultivate it in. As far as media, the bacteria should grow in nutrient broth (as nutrient broth is a very non-selective media). However, as I mentioned in the previous post, MRS is the optimal media for lactobacilli, so if you have access to that in the lab or anywhere, it would be best to use that. 25 mil CFU is a sufficient dose; however, if you want to use different concentrations of probiotics you could certainly use different doses (50 mil and 100 mil CFU). This way you could determine if the lactobacilli have a dose-dependent antimicrobial effect on E. coli.

I hope this helps! Please let me know if you have any follow-up questions on this thread, I am happy to help!

Best,
Brandi