MINT V.S. BACTERIA,
WILL BACTERIA RESIST ?
Arriving in Petnica, I had the idea of making a project linked with medicine and drugs research, as we had the opportunity to do a full microbiology project. When we did the field trip, one of the searcher talked about biodiversity of plants in the region, and he mentioned some ‘antibacterial properties of mint. Having done a bibliography project about antibiotic resistance, this idea hooked me up and I’ve done some research about it.
Several studies showed the antibacterial properties of peppermint and other varieties of mint. The more often, searchers use peppermint oil extract (POE - I need to do an abbreviation because I will talk A LOT about it). This extract concentrates chemical compounds such as menthol or menthone that are dangerous for bacteria. I wanted to do the same kind of study, and compare the impact of POE on both the growth and the survival of bacteria, and compare the results of two different species, one gram negative () and one gram positive (). So I came up with this question : What is the impact of POE on bacterial growth and survival of E. coli and B. subtilis ? The goal was to determine if POE was an efficient antibiotic for these strains, and if yes, at which concentration.
The protocol to study if it was bacteriocide (kills the bacteria) was a protocol based on the CFU (if you don’t know what this is, I advise you to check this website which is really comprehensive, or take a biology course). Basically, I would expose bacteria to POE, at different concentrations, and perform a classical CFU afterwards. Unfortunately, technical issues gave me unrelevant data to use for any conclusions.
The other protocol, to study if POE was bacteriostatic (make bacteria unable to grow or divide) consisted in spreading bacteria over a plate, and then disposing a paper disc soaked with POE at different concentrations on this same plate. After incubation, I would measure the surface where bacteria didn’t grow, called “inhibition zone”.
My data plotted looked like this :
On this graph, you can see the different surfaces of inhibition zones (in cm²), according to the concentration of POE. It presents the results for both B. subtilis and E. coli. The concentration 1 for B. subtilis is not shown on the graph because no bacteria grown in this case. The two types of points represents the two species as you can see on the legend. For each concentration on each species, I’ve made three replicates (measures in the same conditions), this is why there is always three times the same kind of point for a single concentration.
As we can see, controls show a clear difference of values between them (C=0 and C=1), and it seems that the values of surface of inhibition are getting higher with the concentration.This tendencies cannot be shown statistically, as I lack of data (but you always lack of data, right ?)
I can conclude from these results that POE does have a negative impact on bacterial growth, for both E. coli and B. subtilis. It seems that the more concentrated is POE exposure, the more it inhibits the growth of both species. However we can’t see a clear difference between gram + and gram - results. Finally, as further experiments, I would expand my range of bacterial strains to some multi-resistant strains, and compare efficiency of POE with a classical antibiotic. Could we use in the future, antibiotic based on POE for some infections ? Why not ? It’s cheap, easy to grow and it smells quite good !
If you want to know more…
Get an insight on research which is done in this field :
-Basheer A. Al-Sum, Abdullah A. Al-Arfaj. Antimicrobial Activity of the Aqueous Extract of Mint Plant. Science Journal of Clinical Medicin. Vol. 2, No. 3, 2013, pp. 110-113. doi: 10.11648/j.sjcm.20130203.19
-McKay, Diane L., and Jeffrey B. Blumberg. "A review of the bioactivity and potential health benefits of peppermint tea (Mentha piperita L.)." Phytotherapy Research 20.8 (2006): 619-633
-Singh, Rajinder, Muftah AM Shushni, and Asma Belkheir. "Antibacterial and antioxidant activities of Mentha piperita L." Arabian Journal of Chemistry 8.3 (2015): 322-328
-Thomson Healthcare (2007). PDR for Herbal Medicines (4th ed.). p. 640
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