Science Buddies: "Ask an Expert"

Hello,

I am doing a project on the effectiveness of natural vs. pharmaceutical antibiotics against E. coli. For the pharmaceutical antibiotics, I have purchased pre-impregnated disks. However, for the natural ones, I have bought the tablets for them, but I need to dissolve them in distilled water to make a solution to dip sterile disks into. I am trying to figure out a way to standardize the concentrations of these solutions to have accurate results. For the pharmaceutical antibiotics, they have standard disk concentrations which they are sold in. I am wondering how they standardize these disk contents because they seem arbitrary (they have no correlation to MIC), because this could help me figure out how to concentrate my natural antibiotics. I could pick a standard concentration (e.g. 250 mg/ml), but this may throw off my comparison with the pharmaceutical antibiotics.

Thank you.

Hi,

This is a great project, and it’s good that you are considering the details on preparing your own antibiotic disks.

First, here is a Science Buddies project guide for this topic:

https://www.sciencebuddies.org/science- ... p021.shtml

For preparing the disks, you will need an absorbent filter paper that you can cut into disks using a paper punch. Here are the possibilities from this website. You might want to contact the supplier of the standard disks and request samples for your project if the filter paper is not readily available:

http://www.scribd.com/doc/7004714/antib ... reparation

“Four types of paper, namely blotting paper made from imported raw materials but is locally manufactured, Whatman Filter paper #3, Whatman Chromatographic #2 and #3, and Neigele chromatographic paper which are all imported were selected for preparing the disks. The selections were based on its ability to uniformly absorb sufficient volumes of antibiotic solution. These materials including imported blank disks were initially tested for presence of inhibitory activity. Commercially available antibiotic disks (BBL) served as the control.”

Next is the question about how to apply the antibiotic to the disks. The following paper describes a specific technique using a suspension of crystals that gave better results than using a solution of the antibiotic:

http://www.ncbi.nlm.nih.gov/pmc/article ... 1-0130.pdf

Since you are working with unknown samples, you might want to use more than one concentration of you natural antibiotics.


Please let me know if you need any additional information.


Donna Hardy