Can we treat antibiotic resistant bacteria with plants?

6 min readFeb 3, 2019

More than 700,000 people worldwide die annually from infections caused by drug-resistant bacteria (CDC). One major contributor to antibiotic resistance is the overuse of antibiotics in agricultural practices which can facilitate the development of bacterial resistance through the spread of infected livestock waste. This study describes a simple method of using targeted plant extract cocktails to inhibit the growth of antibiotic resistant Escherichia coli (E. coli) in livestock fecal matter.

Now for some history

The medicinal properties of plants have been utilized for thousands of years across the world, by different cultures, and for a wide variety of purposes. Bacterial and fungal sources have been relied on for the production of antimicrobials since the advent of antibiotics in the late 1920s. With the increasing amount of antibiotic resistant infections, in part due to their misuse and limited life span, it is critical to investigate potential available alternatives. It is estimated that there are around 250,000 to 500,000 species of plants on Earth. Plants have the ability to synthesize compounds such as alkaloids or phenols that can serve as plant defense mechanisms against predation (i.e. microorganisms). Certain phytochemicals have useful antimicrobial properties that could be utilized as alternatives to antibiotics becoming rendered ineffective due to resistance.

My motivation

When I approached this topic back in 2016 my motivation came from researching the alarming problem of antibiotic resistance. I realized that 70% of our antibiotics are given to livestock, and while not all of these can lead to resistance in humans (i.e. ionophores used for improving feed efficiency and body weight in cattle), a large amount can. This can happen in a variety of ways. The waste from livestock contains antibiotic residue that can spread when it gets into bodies of water, or is used as fertilizer for other products like growing vegetables.

In a new study led by Diana Aga, PhD, Henry M. Woodburn Professor of Chemistry in the University at Buffalo College of Arts and Sciences, “two of the most elite waste treatment systems available today on farms do not fully remove antibiotics from manure.

Both technologies — advanced anaerobic digestion and reverse osmosis filtration — leave behind concerning levels of antibiotic residues, which can include both the drugs themselves and molecules that the drugs break down into”.

The goal of this study

The goal of my study was to investigate if plant extract cocktails (basically mixtures of plants that can act synergistically together to increase their effectiveness) could be used to inhibit the growth of antibiotic resistant bacteria present in livestock fecal waste. I wanted to see if these extract cocktails could provide an effective waste treatment, and if they could be utilized to treat resistant bacteria.

Here was my hypothesis:

“If single and multidrug resistant strains of E. coli are exposed to a variety of plant extracts (Hydrastis canadensis, Artemisia annua, Gly- cyrrhiza glabra, Juniperus communis berries, Cryptolepis sanguinolenta and Bidens pi- losa), then the mean reduction in bacterial colonies by use of targeted plant extracts (used in combination and specific ratios) will exceed the mean reduction produced by other plant extracts and antibiotic and ethanol controls”.

I selected a total of 6 individual plant extracts based upon: published scientific literature and texts identifying antimicrobial properties and com- pounds, toxicity levels in clinical trials, availability, and potential synergistic properties. Antibiotics selected for comparison to extracts are the most widely used antibiotics in livestock health care that also have implications in human health care (tetracycline, sulphonamide, streptomycin and nalidixic acid).The 6 extracts were used individually, in combinations, and specific ratios (targeted extract cocktails) to identify the most successful alternative to single and multidrug resistant strains of E. coli. The most successful targeted extract cocktail was used to inhibit the growth of antibiotic resistant E. coli present in live- stock fecal matter, a method through which resistance can spread to humans if pathogens are left untreated.

Here’s what I found:

A total of 25 different individual and extract cocktails were screened using a Kirby-Bauer Disk Diffusion Assay to determine their effectiveness in inhibiting the growth of Q-50 (nalidixic acid resistant), SSuT (tetracycline, streptomycin, and sulphonamide resistant), and Q-63 (antibiotic susceptible) strains of E. coli. It was determined that the most effective extract tested was a cocktail of 87.5% Cryptolepis sanguinolenta and 12.5% Hydrastis. All strains of E. coli were found to be highly susceptible to this cocktail, indicating its effectiveness at successfully inhibiting the growth of E. coli strains with multiple antibiotic resistances. Additionally, when this cocktail was used as a treatment on bovine fecal matter, it exhibited a 3–5 log (>99.9%) reduction in antibiotic resistant E. coli growth in comparison to the control groups, thus demonstrating the high potential of this targeted cocktail as an effective, environmentally sound sanitization treatment for fecal matter. Applications can be extended for other sanitization uses in the agricultural, food, and healthcare industries as well as a potential alternative to antibiotics that is effective at inhibiting drug-resistant bacteria.

Strains of the resistant bacteria used for testing with the plant extract cocktails

Plant extract cocktails placed on disks so all the alcohol could be evaporated out of the extracts — so it would not impact the tests. The alcohol was needed to extract certain compounds from the plant.

Here is an example of a **Kirby**-**Bauer disk diffusion** susceptibility test. I placed the disks on the plates with the antibiotic resistant bacteria, and measured the zones of inhibition (basically how large of an area was cleared away from the tested extract/antibiotic).

Here are the samples of fecal matter I used with each extract cocktail. I kept these samples in a fume hood with similar conditions they would experience on a farm.

What you can do

You can read my detailed research procedures, which is basically a long guide to how I conducted all my tests. I’m publishing the link here in hopes that we can expand the research into the antimicrobial properties of plants, and start looking more towards nature when treating diseases. This is just one study, but I think it raises interesting questions about combating resistant bacteria with plants. I am also sharing a 1 page PDF summary of my work — bear in mind some of the visuals are a tad fuzzy, but I think the overall point gets across.

I presented my research at various science events like the INTEL International Science and Engineering Fair, placing Second in Microbiology in the world. This research was all done when I was 17 years old in high school, and it was funded through generous donations after reaching out to local colleges and getting lab access at a health and food safety lab. I taught myself all the microbiology techniques, collaborated with various professors, scientists, and lab technicians to increase the accuracy of my work and received a lot of good input throughout my journey. Many of the strains of resistant bacteria used in this study were found in livestock waste, and I personally went to many farms to collect fecal matter samples when testing the effectiveness of the extract cocktails on the resistant bacteria. We are facing some scary times in our world with the rise of resistant bacteria, and I think now more than ever we could benefit from looking into alternative forms of research.