CAES professor is using nanoscience to combat foodborne listeria

Ask any scientist who studies foodborne illnesses to name the bacteria, virus or parasite that causes them the most sleepless nights, and near the top of their list will be these two scary words: listeria monocytogenes.

Present in soil and water, the bacteria called listeria wreaks a kind of havoc that goes well beyond the garden-variety “I think I ate some bad potato salad” illness that all of us have experienced at one time or another. What starts as flu-like symptoms up to a month after ingesting it can progress to confusion, loss of balance and convulsions as the listeriosis infection spreads throughout the body. According to the Centers for Disease Control and Prevention, listeria is the third leading cause of food poisoning-related deaths in the U.S., killing about 260 of the roughly 1,600 people who ingest it. It’s especially deadly for newborns, the elderly and people with compromised immune systems.

In 2020, for example, deli meat containing listeria infected a dozen people in Florida, Louisiana, Massachusetts and New York. All 12 were hospitalized, and one died.

Leonard Williams, Ph.D., from the College of Agriculture and Environmental Sciences doesn’t want you or anyone else to get listeriosis. In fact, he and his colleagues are spending quite a bit of time figuring out ways to keep you safe from it.

Williams is director and professor of food safety and microbiology at N.C. A&T’s Center for Excellence in Post-Harvest Technologies on the North Carolina Research Campus in Kannapolis. He and one of his doctoral students, Akbar Bahrami, are joining researchers in the U.S. and abroad to consider the impact that antimicrobial compounds could have on protecting consumers from listeria. 

The work was funded in part by a grant from the U.S. Department of Agriculture’s National Institute for Food and Agriculture.

The research, now in its early stages, eventually will explore how to achieve this through encapsulated technologies, which in this situation means embedding antimicrobials directly into the food or the packaging. The process makes use of nanoscience, the use of ultra-small particles to enhance properties.

Food companies have been using microencapsulation or nanoencapsulation for years to add flavor, aroma or even nutritional value to foods. And food scientists have tried various methods over the years to control the growth of listeria in food — including sterilization, which can change the way the food looks or tastes; and heat, which can’t be used on fresh fruits and vegetables.

Using encapsulated technologies to combat listeria is something new. It also has the potential to save lives.

“This is a very, very long-term project, and there are so many avenues that we’re going to explore,” said Williams, a Greensboro native and graduate of Smith High School. “Before we actually go deep into the nanoscience, we have to know how the actual strains (of listeria) respond to those antimicrobials.”

Testing for pathogens

So first things first: Williams’ team had to go grocery shopping.

By his count, his students and research assistants brought into the lab more than 6,000 food samples — eggs, cheeses, milk, dried foods, leafy vegetables, ready-to-eat products and more — from grocery stores, farmers markets and roadside stands. “We’re trying right now to get a profile of all the foods that are considered to be high risk for listeria and look at the prevalence and incidence of listeria in these products,” he said.

Then they tested the samples for listeria monocytogenes, the most deadly form of listeria, but also looked for four other dangerous strains through a process called genotyping. The positivity rate was .9 percent, which is roughly the national average. But listeria is a zero-tolerance pathogen, which means none of the samples should contain the bacteria.

With those positive samples in hand — the gloved hands of heavily protected scientists, mind you — the team sets out to find how resistant the five different strains of listeria are to antimicrobials. “Research has shown that one strain of listeria does not respond the same way to treatments that another strain of listeria does,” Williams said.

He and the other researchers conduct highly complex rounds of antibiotic testing on the listeria samples. Among the things they’re considering: Are naturally occurring antimicrobials more effective than synthetic ones? What’s the minimum concentration necessary to kill 50 percent of the listeria? To kill 90 percent? What other foods might interfere with the antimicrobial’s impact? How long are time-released antimicrobials effective? How do these antimicrobials hold up under environmental stressors, such as thermal processing?

A bright future

The work already has led to nine different academic papers. For example, some early findings, published in Critical Reviews in Food Science and Nutrition, show that encapsulation strategies may be more effective against listeria than naturally occurring antimicrobials, which are scarcer, more expensive and less stable. 

And the team isn’t done. Williams emphasizes that this is slow, incremental work, but said that eventually the research could lead to a patent for a new kind of encapsulated technology that adds listeria-fighting microbes into food or onto packaging by coating it with antimicrobial nanoparticles. 

Across the world, other scientists are doing similar work on other types of foodborne pathogens, he said. The technology has great potential, according to Williams, particularly in a culture that values easily accessible packaged foods.

“There are researchers out there who are focusing a great deal of their attention and time on trying to develop rapid methods to detect and control pathogens in ready-to-eat food products,” he said. “It takes time to develop these technologies. We still have a lot of work to do, but the future is extremely bright when it comes to developing new value-added products that are safe for consumption and can be readily consumed with very minimum heating.”