Few words strike horror into the hearts of food producers like “Listeria,” and a new study out of Purdue University’s Department of Food Science carries the unwelcome news that the bacteria can live within the tissue of romaine lettuce.
Research led by Professor Amanda Deering, PhD, reveals that Listeria monocytogenes bacteria is able to gain entry to romaine lettuce through cracked seed coats, tears in root tissue, and other damage to the plant. It can subsequently survive within the tissue of lettuce throughout each stage of the plant growth process.
“We know the Listeria is naturally present on the soil so the assumption would be that it could contaminate the surface of the plant during production or harvest,” Dr. Deering explains. “I have published research, as well as others, that has shown the ability of human pathogenic to internalize into plant tissue. This is the first study, however, that has demonstrated that Listeria can internalize within lettuce tissue. Once the bacteria are inside, postharvest sanitization treatments that are typically done in the industry to wash/clean the lettuce will not likely be effective.”
Listeria bacteria can easily be killed by heat, meaning many foods exposed to it during the growing process may be made safe, but the problem Dr. Deering notes is that lettuce is consumed raw. Careful not to overstate risk, she underlines the principal concern is for consumers who are immunocompromised.
“From a production standpoint I don’t think there can be any changes made to inhibit the potential of Listeria contamination,” she says. “Plants grow in soil, and Listeria is naturally present in the soil, so there’s not really a way around it. I think my research points to the fact that if Listeria is able to internalize in the plant tissue then what we typically do for postharvest sanitization methods won’t do much, however, it will help reduce the bacteria that are present on the outside of the lettuce leaves. Growers need to continue to follow Good Agricultural Practices and consumers need to keep in mind there is a risk to eating certain food.”
In a strongly worded response, Dr. Jennifer McEntire, PhD, VP Food Safety and Technology for the United Fresh Produce Association in Washington, D.C., argued this study actually contains some good news. Dr. McEntire begins by underlines Dr. Deering’s point that Listeria is so much a part of soil it is considered ubiquitous.| | | Next → | Single Page
About Jesse Staniforth
Jesse Staniforth is a Montreal-based freelance journalist, writer, and editor covering a variety of different beats. He reports regularly on Indigenous issues for The Nation magazine, serving the Cree Nation of Eeyou Istchee, as well on Information Security issues for SC Magazine. His stories have appeared in a wide variety of other publications, from the Toronto Star and Metro News through AskMen.com and University Affairs. After editing several thousands of pages' worth of food preparation training materials for a hospitality industry group, he grew fascinated with the subject of food safety. Reach him at email@example.com.