Probiotics, the microorganisms in yogurt and other fermented foods that are known as beneficial bacteria, could be modified to stop Listeria cells from passing through intestinal walls and into the bloodstream, according to Purdue University scientists.


“Based on the research, it looks very promising that we would get a significant reduction in Listeria infections,” Arun Bhunia told the Purdue University News Service Monday.

Bhunia’s findings were published this month in the journal PLoS One.

The research team –  Bhunia, professor of food science; Mary Anne Amalaradjou, a Purdue postdoctoral researcher; and Ok Kyung Koo, a former Purdue doctoral student – envision a day when people most vulnerable to Listeria infection could be given a pill or probiotic drink to minimize their risk.

Listeria can contaminate processed meats like hot dogs and cold cuts, and unpasteurized milk and cheese are particularly likely to contain the bacterium. The 2011 outbreak caused by Listeria-tainted cantaloupes was the deadliest in the United States in nearly 90 years.

Each year in the U.S., about 1,600 people become seriously ill with listeriosis and of those about 260 die. Listeriosis primarily affects pregnant women, newborns, older adults and those with weakened immune systems. Once in the bloodstream, even small doses of Listeria can cause fever, muscle aches, nausea and diarrhea, as well as headaches, stiff neck, confusion, loss of balance and convulsions if it spreads to the nervous system. It can also cause miscarriage and stillbirth in pregnant women.

Listeria binds to intestinal cells using an adhesion protein and passes into them, “acting as a sort of gateway to the bloodstream,” according to the Purdue newsroom.

The researchers found that probiotics alone were ineffective in combatting Listeria, so they stole a trick from the bacteria’s own playbook. By adding the Listeria adhesion protein to the probiotic Lactobacillus paracasei, they were able to decrease the number of Listeria cells that passed through intestinal cells by nearly half — 46 percent — a significant decrease in the amount of the bacteria that could infect a susceptible person.

With the adhesion protein added, the modified probiotic then attached to the intestinal cells, crowding out Listeria.

“It’s creating a competition,” Bhunia said. “If Listeria comes in, it doesn’t find a place to attach or invade.”

The researchers’ initial results came from tests on human intestinal cells. The next step would be animal testing, Bhunia said, which would allow him to see whether different doses would have a greater effect.