When antibiotics fail, can the answer be in the kitchen garden?
By Pranandita Biswas
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Antibiotic resistance— the ability of bacteria and other disease-causing microbes to survive exposure to antibiotics— is a major challenge in healthcare and sanitation, costing millions of lives every year. With the widespread use (and misuse) of antibiotics, bacteria mutate and adapt to these drugs ever faster. Nic Thomas, a PhD student in the Department of Chemical and Biomolecular Engineering at UMass Amherst, is investigating a novel solution to the problem using essential oils.
Why essential oils? “An essential oil has hundreds of different chemicals that can dissolve the cell membranes of bacteria,” Thomas explains. Bacteria would thus take much longer to develop resistance to essential oils than to single antibiotic chemicals.
Thomas’ fascination with science goes back to his childhood. As a high schooler, he enjoyed both math and chemistry. Majoring in chemical engineering was a natural choice. As an undergrad at the University of Maryland, Thomas had the opportunity to intern in multiple research labs, including at a pharmaceutical company making contact lenses. There, he discovered his penchant for detail-oriented, hands-on experimental work. With the encouragement of his mentors, he embarked on his PhD to study biomaterials at UMass, for which he won the Spaulding–Smith Fellowship awarded by the university.
At UMass, Thomas works with materials engineer Dr Jessica Schiffman to make antibacterial materials using essential oils. “Since essential oils are volatile, they evaporate into the air very quickly,” he says about the main challenge in his research. To solve this problem, the oils must be “immobilized,” i.e., they must be chemically bound to more stable materials. For example, Thomas, in collaboration with scientists from Germany and Spain, recently developed a water filter with antibacterial essential oils immobilized onto it.
To understand how this works, imagine water filters as very fine sieves made of a mesh of hollow nanofibers, i.e., fibers that are a few nanometers wide. The scientists first immobilized the essential oils onto ring-shaped molecules known as beta cyclodextrins, which they then embedded inside these hollow nanofibers. The oils were sourced from plants such as thyme and peppermint, and some of these strongly hindered the growth of common bacteria such as E coli.
For his next project, Thomas is making adhesive antibacterial films for exposed surfaces by immobilizing essential oils onto the films. These antibacterial films will not only kill existing bacteria, but also prevent new ones from growing, thus reducing cleaning and disinfection costs. This is critical in hospitals and other environments where the risk of infection is high. To make these films, he uses the biochemical dopamine, which is commonly known as a neurotransmitter, but which also exhibits adhesive properties when polymerized. Polymerization is when smaller molecules link with each other to form larger molecules, which are called polymers. Adhesive polydopamine is a bio-inspired polymer; for example, in nature, mussels have polydopamine in their feet, which helps them attach to rocks.
Since the polymer films are formed in a water-based solution, it is challenging to incorporate essential oils into them because oil does not dissolve in water. Thankfully, polydopamine displays an interesting property that helps solve this problem.
“[Polydopamine] … is amphiphilic, meaning that it has [both] hydrophilic (water-attracting) and hydrophobic (water-repelling) parts,” Thomas explains. “We’re hypothesizing that the hydrophobic part of the molecule is interacting with the essential oil.” Essentially, the hydrophilic part of the molecule keeps it dissolved in the water-based solution in which the film is formed, while the hydrophobic part adheres to the essential oil. This makes it possible to “dissolve” the essential oils in the film. Thomas is now experimenting with using different essential oils to improve the performance of the films.
Across his projects, Thomas is driven by his passion for sustainability. Through his research and outreach, he hopes to highlight the threat posed by antibiotic resistance and find sustainable alternatives to traditional antibiotics. “Now it’s a great idea to move to a more natural way of killing bacteria,” he says. In the long run, he hopes to extend this work into other applications, such as in home-care products, replacing harsh chemicals with natural ones that are more environmentally-friendly.
Outside the lab, what does he find the most rewarding about the PhD? Thomas feels fortunate to have found a supporting and warm community at UMass through his lab and friendships. Although he finds communicating his research to be a challenge, partly because of a speech impediment, he has gained confidence thanks to the support of his supervisor, Dr Jessica Schiffman. Ultimately, Thomas finds motivation in his mission of improving human health, of “making a very, very small contribution to the world.”