The more we use antibiotics, the less effective they become, leading to the appearance of "superbugs" that are resilient to the drugs' antibacterial properties.
Every year, as many as 2 million people in the United States are infected with a drug-resistant bacterium, and most of these infections occur in hospitals.
Mohan Jacob, the head of the Electrical and Electronics Engineering Department at James Cook University (JCU) in Queensland, Australia, explains that a large number of these bacteria are found on the "biofilm" that forms on medical devices.
Biofilm infections are a growing health concern in their own right. "Just in the U.S., about 17 million new biofilm-related infections are reported annually, leading to approximately 550,000 fatalities each year," Prof. Jacob says.
"It's thought about 80 percent of worldwide surgery-associated infections may relate to biofilm formation," he adds.
So, in the context of antibiotic resistance, is there a way to stop the bacterial biofilms from forming on medical devices without relying on antibiotics?
Researchers believe so. Plants naturally produce antimicrobial molecules, and in recent years, scientists have used nanotechnology to harness the power of these compounds to create antibacterial coatings.
The plant compounds are called plant secondary metabolites (PSMs) as they are not essential to a plant's survival and functioning.
A central challenge to creating antibacterial coatings from PSMs, however, has been converting the compounds' natural liquid state into a solid state without losing any of their antibacterial properties.
Now, a team of researchers led by Prof. Jacob found a way to turn PSMs into bioactive coatings for medical devices.
Their findings were published in the journal Polymers.
Turning liquid tea tree oil into a solid coating
Prof. Jacob further explains what PSMs are, saying, "They're derived from such things as essential oils and herb extracts and they have relatively powerful broad-spectrum antibacterial activities."
"PSMs are a low-cost renewable resource available in commercial quantities, with limited toxicity, and potentially, different mechanisms for fighting bacteria than synthetic antibiotics," he adds.
Study co-author Kateryna Bazaka, an adjunct senior research fellow at JCU, explains the procedure through which the scientists were able to tackle the challenge of turning liquid PSMs into a solid coating of polymers.
Polymers — such as the naturally occurring rubber and cellulose, or the man-made Teflon and polyurethane — are characterized by a resistant, "chain-like structure."
"We used plasma-enhanced techniques within a reactor containing the essential oil vapors. When the vapors are exposed to a glow discharge, they are transformed and settle on the surface of an implant as a solid biologically active coating."
"These have shown good antibacterial properties," she continues.
Plasma polymerization techniques have been used to create bioactive surfaces for a few decades now. In the new study, the researchers focused on converting the PSMs of tea tree oil, also known as Melaleuca alternifolia.
Bazaka explains just why the plasma technique is particularly useful for converting PSMs into solid, bioactive coatings. She says, "The main advantage of this approach is that we are not using other chemicals, such as solvents, during the fabrication process."
"As such, there is no threat of potentially harmful chemicals being retained in the coating or them damaging the surface of the material onto which the coating is applied. It also makes the fabrication process more environmentally friendly," she adds.
If tea tree oil components end up being routinely used to protect the surface of medical devices, millions of infections could be prevented each year.