September 8th, 2015Some bacteria are our friends. Without them, we wouldn’t have cheese, beer, wine, pickles, sourdough bread and other delicacies. And the complex ecosystem of many bacterial species living within our guts extract and manipulate nutrients in our food that we need to survive. People also need the microbes to break down sewage, contribute to healthy soil for growing crops and produce methane and other fuels.

But the same bacteria in the wrong place–like in a bag of spinach, for instance–are our enemies. They cause food to spoil and lead to potentially life-threatening infections when they invade the body. Illustrations of this love-hate relationship are all over the news right now, with salmonella-tainted cucumbers currently sickening hundreds in a number of states and disease outbreaks caused by the common food-borne bacteria E. coli putting dozens more in the hospital in Seattle and Canada.

Scientists are constantly looking for new ways to limit human exposure to pathogenic bacteria in our food. In the latest finding, researchers in Germany and the U.S. might have found a better defense against pathogenic food-borne microbes by making plants produce a type of antibiotic some bacteria use against their competitors.

The study reported yesterday in the journal PNAS revealed scientists had genetically engineered food plants like spinach and beets to produce chemical controls against pathogenic strains of food-borne illness-causing E. coli. They say these plant-made chemicals could be applied to raw foods to slow or stop E. coli contamination before it gets to consumers.

E. coli “is one of the leading causes of bacterial enteric infections worldwide,” write Anatoli Giritch, a molecular biologist at Germany’s Nomad Bioscience, and colleagues in their study. “These illnesses have been linked to consumption of contaminated animal products and vegetables. Currently, other than thermal inactivation, there are no effective methods to eliminate pathogenic bacteria in food.”

They investigated a potential solution with more than a hint of irony. Instead of looking at antibiotics or other such controls, they looked at the bacteria itself, focusing on a type of protein called colicin. This group of proteins are produced by certain E. coli strains to kill or inhibit the growth of other E. coli strains. The molecule, which acts on the bacterial membrane and impedes enzyme activity of closely related species, is produced as a way to hinder competition between strains.

The team used engineered bacteria to inject colicin-producing genetic instructions into tobacco, spinach and beet plants. They found that the plants became biofactories, producing significant quantities of the molecule that could then be purified through processing. Next, they applied a solution of pathogenic E. coli onto pork steaks and then put the plant-made colicin onto some of the steaks.

They found that colicin applied at low concentrations to the meat reduced E. coli population growth by two orders of magnitude. Such improvement is a significant advance, especially since the plant-produced colicin is virtually the same as that produced by bacteria already present in the human gut. This means that the body already deals with the chemical regularly and regulatory approval to use it as a food additive should be a straightforward process.

“We show that mixtures of colicins applied at low concentrations are highly and broadly active against all major pathogenic E. coli strains of concern for foodborne illness,” the authors write. “We propose plant-produced colicins as an inexpensive food treatment for the broad control of pathogenic E. coli strains.”

Top Image: Spinach growing via Shutterstock.