Listeria: Deadly Foodborne Threat to Vulnerable Populations

By Chris Healey

A listeria contamination scare has prompted a fruit packing company to issue a voluntary recall of peaches, nectarines, plums, and pluots shipped to Costco, Trader Joe’s, Kroger, Walmart, Sam’s Club, Ralphs, and Food 4 Less. The company—Wawona Packing Co.—issued the recall after an internal bacterial test found listeria on two nectarines. So far, no one has been sickened from affected fruit.

Listeria monocytogenes, the causative agent of listeriosis, is a common foodborne bacterial pathogen. With the ability to thrive in refrigerated foods, it can quickly multiply and spread on foods which have been properly stored and otherwise deemed safe for consumption. It is unique among foodborne illnesses for its tendency to cause miscarriages and encephalitis in sickened individuals.

Although listeria infection is uncommon, fatality rates reach as high as 30%. Several groups are prone to infection – pregnant women, infants, the elderly, organ transplant recipients, leukemia patients, and those with AIDS. The highest infection rates occur in infants younger than one month and adults older than 60 years.

Once ingested, listeria crosses the mucosal barrier of the intestines to the bloodstream. From there, listeria tends to target neuronal and placental tissue. Defenses associated with those tissues, such as the blood brain barrier of the central nervous system, are not effective because infected host cells can slip by unaffected and release bacteria.

CDC surveillance studies in the 1980s brought listeria to the attention of health professionals in the United States. Those studies determined L. monocytogenes was the causative agent of approximately 1850 cases of food poisoning and 425 deaths annually. Since identification, listeriosis incidence and associated death has decreased. Today, the CDC estimates 1600 cases of listeriosis with 260 fatalities yearly.

In 2002, Listeria was responsible for the largest meat recall in U.S. history. An epidemiologic investigation conducted after a listeriosis outbreak determined 54 case patients had consumed sliced deli-style turkey meat tainted with listeria. As a result, over 30 million pounds of food products were recalled.

The largest listeria outbreak occurred in 2011 due to contaminated cantaloupe from Jensen Farms in Colorado. During that outbreak, 147 people from 28 states became ill. Of those cases, 33 died. The CDC website reports a listeriosis outbreak occurrence every year since 2011.

To prevent listeriosis, the CDC recommends consumers rinse raw produce thoroughly before eating. Full recommendations from the CDC can be accessed here.


(Image Credit: Ximeg)

Image of the Week

This week’s image come via Microbiology and Immunology, and is of cell lytic enzymes attached to nanoparticles, which are then used to kill listeria!

“Fighting Listeria with Nanobiotechnology: Using nature as their inspiration, the researchers successfully attached cell lytic enzymes to food-safe silica nanoparticles, and created a coating with the demonstrated ability to selectively kill listeria—a dangerous foodborne bacteria that causes an estimated 500 deaths every year in the United States. The coating kills listeria on contact, even at high concentrations, within a few minutes without affecting other bacteria. The lytic enzymes can also be attached to starch nanoparticles commonly used in food packaging.”

Read more here.