Today we begin our next experiment to test the antimicrobial properties of raw honey, stevia, and high fructose corn syrup. We will begin with extracting different groups of phytochemicals from the stevia plant and the stevia flower. For the raw honey and the HFCS, we will make solutions of different concentrations. We will be using disk diffusion to look for zone of inhibition against E. coli and S. aureus.
A couple of weeks ago we tested xylitol and HFCS. We used the following concentrations: 0, 5, 20, and 25%. There was no inhibition on the disk diffusion against E. coli and S. aureus. But we did observe that the HFCS encouraged growth.
The other test we did with these two sweeteners was to see if E. coli and S. aureus could metabolize xylitol or HFCS. We aliquoted 5 mL of PBS into 6 test tubes. For 2 we added nothing else. For another 2, we added 1.25 grams of xylitol and for the other 2, we added 1.25 mL of HFCS. We inoculated 3 tubes with 100 microliters of E. coli and the other 3 with 100 microliters of S. aureus. The results were interesting. After incubating at 37 C for 48 hours, we observed growth of both organisms in the HFCS. The xylitol also showed growth but not as much. I plated 10 microliters onto a nutrient agar plate of each tube. I did not do any dilutions. After 24 hrs at 37 C, there was too many to count growth on the plate. Plus, either by my error or from contaminated PBS, there was also growth of yeast present on the plates.
Two weeks later, the PBS shows no growth for either organism. The xylitol shows small growth and the HFCS shows moderate growth. We plan to plate for growth but this time will probably take it to the 2nd dilution.
I read some interesting peer-reviewed research papers on the antimicrobial properties of stevia so I am excited about testing this. I will also be learning how to do protein gel electrophoresis and will be doing chromatography.
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