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“Natural Antibiotics” and Bacterial Growth

Holly M Thurman

ABSTRACT

My research was to investigate the effectiveness of claims that alternative or “natural” antibiotics, as they are touted by their advocates, are as effective as traditional antibiotics or effective at inhibiting bacteria growth at all. The methods used were traditional in vitro bacteria growth on nutrient agar and impregnated disks. The results have not shown that any of the samples that were tested were effective to any extent in growth inhibition. Efforts to find new antibiotics would perhaps be better aimed at areas where some of the more recent finds have been made such as lipopeptides or daptomycin rather than spending time on items that do not seem to have reproducible results. (A. Giuliani, G. Pirri, S. F. Nicoletto, 2007)

A. Hypothesis for the chosen scientific question.

If the “natural antibiotic” samples are used on the bacteria then there will be no obvious

interference with growth (no zone of inhibition).

“Natural antibiotics” in this paper shall be referring to the samples of garlic, Echinacea, lavender

oil, ginger, tea tree oil and honey used for testing bacterial growth.

 B.  Literature review of three professional sources that are relevant to the chosen scientific question.

The first article, “The mode of antimicrobial action of the essential oil of Melaleuca alternifolia (tea tree oil)”, did seem to make a good case for the efficacy of tea tree oil being useful as a topical antibacterial and antifungal. Unlike the general spice article, it did seem to contradict itself and went into specifics as to how this oil interfered with cell membrane structure and respiration. They were very specific about not only the bacteria used (only gram positive) but also the media that it was grown on. While some of the discussion was above me as how the tea tree oil affected the bacteria and the candida, I could not find fault with the general presentation of the paper or process. My only criticism without knowing more would possibly be that the research was conducted under the funding of the Australian tea tree oil Research Institute. While this does not guarantee that it is bad research, it does make one perhaps look askance at some findings. (Carson, Hammer, Riley, 2006)

The second article, “Antibacterial activity of natural spices on multiple drug resistant Escherichia coli isolated from drinking water, Bangladesh”, is the second one I chose to review. This paper starts out by mentioning the existence of drug resistant bacteria and how herbals would ostensibly be a choice that could save us from this predicament. This is a puzzling suggestion since many antibiotics are natural substances, the most obvious of these being penicillin which is nothing more than a mold.

The author closes by citing many other sources that seem to prove the original contention that these spices are useful for many ailments but much of this is not proven by his own paper and appears artificial and forced. (Rahman, Parvez, Islam, Khan, 2011)

type of bacteria) and a few (mint extract and eucalyptus oil) that seemed to do well against all the organisms. (N. Yadav, E. Yadav, J. Yadav, 2012)

1.  Discussion of the underlying scientific concepts of the design.

There are several ways that antibiotics kill bacteria, penicillin prevents the regrowth of the cell wall and tobramycin prevents the formation of proteins. However they may work, antibiotics will generally create a zone of inhibition (an area around the disk that is clear of bacteria) that is visible around bacteria. Exceptions can occur, of course, depending upon the type of bacteria. Tobramycin  (the traditional antibiotic used here) is used to treat primarily gram-negative bacteria but can also target gram positive.

Eight samples of bacteria were taken and grown on petri dishes in nutrient agar. After approx. 48 hours a streak plate was taken from one sample in order to have a  consistent bacteria with which to test all of the samples and use as controls. From this plate a divided (quadrant) plate was used for

each sample and controls. The plates were thoroughly inoculated, allowed to sit for approx. 10 minutes and then had a disk of either a sample of the “natural antibiotic” placed in the center of each quadrant or a disk of tobramycin or no treatment. Three plates were used for a total eight samples (including the tobramycin) and four controls. Inoculation was done with fire sterilization and incubation was in an incubator at a temperature of approx. 39C.

The plates were allowed to incubate for approx. 48 hours and then inspected and photographed. All

samples appeared to be without a kill zone, indistinct or otherwise, except sample VIII that had a kill zone of 3mm from the edge of the disk.

The samples were prepared by adding a small amount of distilled water if the sample was dry or very viscous (the echinacea, ginger and honey) and then soaking the disk in the mixture of herb and distilled water for approx. 3 minutes. For the oil of lavender, tea tree oil and tobramycin, the disks were soaked approx. the same amount of time without dilution. With the garlic, a clove was cut in half and the disk inserted in the two halves to soak in the garlic juice produced by this cut for approx. 5 minutes.

D.  Results of the completed experiment:

1.  Summarize the results.

All of the sections except section VIII, were healthy and untouched by any kill zone. The

tobramycin had a zone of inhibition that was unclear with a radius of  3mm. No retarded growth

area could be seen around the discs in area except for VIII. Section VIII was the disc that was soaked in tobramycin, the antibiotic.

2.  Analyze the data using mathematics and appropriate technology.

The kill area around the tobramycin (sample number VIII) was roughly 3mm. This is the measurement from the outside ring of the disk.

E.  Do the findings support the hypothesis?

My findings support my hypothesis quite well. I had some doubts as to whether there might be some zone of inhibition around the honey or the essential oils, due to some positive reports on the efficacy of honey and the general caustic nature of essential oils in general but I was not able to show that these actually retard the growth of the bacteria that I grew.

1.  Describe limitations of the investigation.

The first limitation of my research are that I did not have control over the quality of the “natural anti-biotic” samples. The natural supplement industry is not regulated and so it is difficult to be certain as to the purity of the oils or herbs or even as whether the herb or oil shown on the label is the one being used. The honey and garlic (fresh garlic clove was used) are far more certain in their purity because they are foods, at least. Another aspect of this limitation could be that a certain “better form” should have been used that could have produced better results, such as oil of Echinacea instead of the herb itself.

The second limitation of the experiment is that the amount of sample was not measured. Although, of each item only  enough was used to soak the paper for testing, the actual amount used for each was not measured and this could be seen as a perhaps an error (not enough of Echinacea was mixed perhaps it would be argued). This is a negligible argument, in my opinion, since each paper was coated with the oil or herb thoroughly and mixed with only minimal amounts of distilled water (enough to ensure soaking and adherence). Every attempt was made to ensure that each substance

was available to kill bacteria if it was able.

2.  Recommended areas for further research.

While there seem to be many studies that show varying degrees of success or failure with using

non-traditional antibiotics and along with that there is plethora of speculation (along with outright statement of certainty) as to what mechanisms are at work there seems to be little continuing investigation into these supposed mechanisms. By this I mean, if, indeed, oil of eucalyptus is an effective antibiotic then what within it is the effective antibiotic? There are certainly things that exist that kill bacteria that would work in vitro that one would not wish to use in vivo. If there is a certain ingredient or chemical within the item that may be helpful then perhaps some research into that aspect should be done. I would be interested to know if perhaps some of the good results from some items were perhaps from there acidity, this being something that bacteria are usually adverse to.

The search for an antibiotic will be an ongoing process simply because of living nature of bacteria and will not stop because we find garlic or certain oils helpful. Latest research seems to show that bacteria have known how to fight most of their natural killers for quite some time and I suspect that if any of these items mentioned in much of natural antimicrobial literature were useful then we would be meeting up with bacteria that were resistant to it. Perhaps we simply haven’t run into them quite yet. (V.M. D’Costa, C.E. King, L. Kalan, M.Morar, W.W. Sung, C. Schwarz, D. Froese, G. Zazula, F. Calmels, R. Debruyne, G.B. Golding,  H.N. Poinar, G.D. Wright, 2011) N. Yadav, E. Yadav, J. Yadav, (2012). Antimicrobial activity of selected natural products against Gram-positive, Gram-negative and Acid-fast bacterial pathogens. Alternative Medicine Studies, volume 2, e12.