Science: Gut bacteria may protect from Listeria

To food industry sanitation experts, there isn’t a term much scarier than “Listeria.” Especially lately, “Listeria monocytogenes.” Scores of recall notices hit the news on a regular basis.

The bacteria can cause severe illness in people who eat food contaminated with it, and causes great difficulties for food producers. It’s a hardy, adaptable organism that can survive and thrive in many environments, especially cold, wet surfaces (like refrigerators — yikes). Produce has a high risk factor, especially convenience items like bagged salads and fresh cut fruits and veggies.

For the most part, getting sick from Listeria is an unpleasant experience, but healthy adults usually recover within a few days without extensive medical treatment. However, for very young, elderly, pregnant and otherwise immunocompromised people, especially cancer patients, infection can be much more dangerous.

Normally, Listeria bacteria remain in the gastrointestinal tract, but in severe cases, it can escape into the rest of the body, causing blood poisoning, meningitis or even death.

Researchers have found, however, that gut bacteria may be able to fight against the most severe infections. This knowledge might provide answers in treating listeriosis by helping to develop probiotics that protect those most susceptible to infection.

Gut bacteria are the usually harmless microorganisms that dwell in the digestive tract. They even have a helpful relationship with their hosts, by toughening the immune system and preventing the development of harmful bacteria.

The team found that using antibiotics to disturb the natural gut microbiome in mice made them more susceptible to L. monocytogenes. This effect was pronounced in mice with weakened immune systems, and those that had been treated with common chemotherapy drugs.

The chemotherapy-treated mice are key — human patients with certain forms of cancer are as much 1,000 times more likely to get severely ill from Listeria than healthy people, due to the immunosuppressive effects of chemotherapy.

Once researchers identified certain gut bacteria that had positive effects, they transferred them to the mice. The bacteria limited the ability of Listeria to colonize in the gastrointestinal tract and beyond.

Researchers believe that gut bacteria-based probiotics can help not just cancer patients, but also pregnant women and anyone else expected to face a compromised immune system.