al activity by themselves,” Jeong recalls. “It was such a surprise, you don’t expect to get meaningful data from your control group.” Researchers already knew that chitosan in its raw form had antimicrobial properties under certain conditions, but no one had yet looked into its properties when it’s engineered into micro-sized particles; which is important, because microparticles will sometimes behave entirely differently from their parent material.
The chance discovery landed Jeong on EPI’s radar, and he was recruited with a position split between the EPI and UF’s Institute of Food and Agricultural Sciences animal sciences department. First on his agenda? Figuring out why chitosan nanoparticles are so good at killing pathogenic E. coli O157:H7.
KC Jeong in his EPI microbiology lab.
Using genetics and animals, he soon discovered that the miniature chitosan bits essentially plug up “gates” in an E. coli’s bacterial cell wall that provide a portal to accept nutrients. The structure of the E. coli bacterium’s cell wall is also disrupted by the particles, causing further damage and death.
Jeong and his collaborators found that chitosan nanoparticles turned out to be broadly effective against many other disease-causing microorganisms too. Better yet, they did not produce resistance in the bacteria targeted. Jeong’s further work revealed chitosan nanoparticles reduced the presence of various strains of Salmonella enterica in agricultural water. This was eye-opening because livestock can acquire this disease-causing bacteria from drinking water, and then pass it on to people when the animals become food.
But not all particles are created equal, so Jeong studied how to best engineer chitosan nanoparticles to optimize their effectiveness against E. coli O157:H7 without producing resistance. Creating particles smaller than 300 nanometers, and adding other ingredients, turned out to be key.
“It kills bacteria very quickly, like Clorox,” says Jeong. “The beauty of this is that it does not cause antibiotic resistance. It disrupts the cell membrane so fast that the bacteria does not even have time to develop resistance mechanisms.”
It’s fair to ask how safe this new nano-bactericide is for people, given some people’s concerns about the science of nanoparticles. Chitosan is favored as a drug-delivery material specifically because of its low toxicity to humans. But because materials sometimes behave differently when reduced to a nanoscale, testing for safety is important for understanding this material’s efficacy in treating infections in animals and humans. To investigate, Jeong and colleagues performed a risk assessment using animal models. The results showed that when used at concentrations strong enough to have antimicrobial effects, chitosan nanoparticles caused no toxicity to animal and human cells.
After figuring out the underpinnings of how chitosan nanoparticles work against pathogenic microorganisms, Jeong set his sights on how to harness this power to benefit agricultural animals and make animal-based foods safer for people.
Metritis and mastitis are two cattle diseases that plague dairy and beef farmers, costing them millions of dollars per year. Metritis is an infection of the uterine lining caused by multiple microbes. It can strike 20 to 40 percent of postpartum cows and it directly costs the U.S. dairy industry upwards of $600 million annually. Mastitis is an infection of a cow’s mammary tissues, or udder, and it is estimated to cost farmers $110 per cow in lost income.
Beef cattle on a northcentral Florida farm participating in one of Jeong's studies on interactions between livestock, the environment, and bacteria. (Courtesy of the Jeong lab.)
But worse than the lost revenue, cattle are experiencing an increase in multi-drug resistant bacteria relevant to these infection types. This is worrisome for human health too, because bacteria are adept at sharing genes useful to their survival. Jeong has sought to characterize the specific types of bacteria and drug resistance genes involved in these infections, in order to bette