Ying Xia and Zongyu Zhang
Ying Xia, postdoctoral research associate in materials science and engineering (right), shows Zongyu Zhang, graduate student in food science and human nutrition, a cationic polymer liquid dispersion used in casting soybean oil-based antibacterial coatings. Zhang is holding a microbiology culture plate used to test the coatings against bacterial pathogens. Download larger photo

Researchers Create Biobased Coatings with Antibacterial Properties

Michael Kessler, associate professor of materials science and engineering and Biopolymers & Biocomposites Research Team member, has teamed up with Byron Brehm-Stecher, associate professor of food science and human nutrition, and Richard Larock, distinguished professor emeritus of chemistry, to develop soybean oil-based coatings that have antibacterial properties.

 Although there are antibacterial coatings that are commercially available, they are not biobased and they are fabricated by adding antimicrobial chemicals into the coatings. Kessler's research team used soybean oil from the local grocery store to create polymers that are biorenewable and prepared in an environmentally friendly manner without the use of volatile organic compounds. Then they incorporated cationic charges into the polymer structure to make the coatings antibacterial. Cationic compounds have the ability to bind to bacteria and other microbes and disrupt their structure, leading to cell injury and/or death.

"Cationic molecules, such as antimicrobial peptides, are widespread throughout nature, protecting all sorts of animals against bacterial infections. So these coatings are a great example of art imitating life," Brehm-Stecher said.

After Kessler's team produced the coatings, Brehm-Stecher's lab worked to test the coatings' antibacterial performance and to characterize their activities against the bacterial pathogens Listeria monocytogenes and Salmonella Typhimurium. "Together, L. monocytogenes and Salmonella spp. are responsible for 47 percent of foodborne disease-related deaths traced to known agentdqus in the United States," Brehm-Stecher said, explaining the choice of these pathogens. They found that the coatings exhibited strong antibacterial properties against these pathogens.

Polymer films were cast onto sterile paper disk supports
Polymer films were cast onto sterile paper disk supports. The film-coated disks were placed onto agar overlays seeded with the bacteria to be tested and the plates were incubated overnight to allow cell growth. Polymers with strong antibacterial properties inhibited growth of the test strains in the vicinity of the film-coated disks, resulting in clear regions, called "zones of inhibition." These zones were measured (in mm) to provide quantitative data on the antimicrobial efficacy of each film. Download larger photo

These coatings could have applications in many fields where the killing of pathogens or prevention of surface colonization is essential. "These coatings could potentially be used to create an active surface that kills microbes on contact," said Brehm-Stecher. "Control of microbes in a food processing plant or in a hospital operating room is easier if they can be killed before they have a chance to grow and establish themselves in the environment."

Brehm-Stecher said the same benefits might be realized for food packaging, but further work is needed to examine whether any components of the coatings might be able to migrate into the food, which would be undesirable.

The researchers will continue to investigate the performance of these and other coatings against multi-drug-resistant bacteria, fungi and viruses. They will also begin to study how long the antibacterial property will last.