Better Treatment for Listeria?

By Jane Farrell

Researchers have discovered that the pathogen Listeria monocytogenes grows on refrigerated smoked salmon via a different pathway than had been known to do in the laboratory.

The research could lead to reduced incidences of food-borne illness and death, said principal investigator Teresa Bergholz, PhD., of  North Dakota State University, Fargo.

The study appears July 24 in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

In the study, the investigators showed that Listeria monocytogenes grows on cold smoked salmon by using different metabolic pathways to obtain energy from those it uses on laboratory media, even when the media was modified to have the same salt content and pH as the salmon. To grow on the salmon, the bacterium “upregulates” genes that enable it to use two compounds from cell membranes—ethanolamine and propanediol—as energy sources.

Listeria monocytogenes, as well as Salmonella, is known to use those same genes to grow within a host—in the gastrointestinal tract, and on macrophages (large white blood cells) . “There may be ways we can use this information to control the pathogen both in foods as well as in infected people,” said Bergholz. “Understanding how a foodborne pathogen adapts to environmental stresses it encounters on a specific food could allow food microbiologists to develop inhibitors of metabolic or stress response pathways that are necessary for the pathogen to grow or survive on that product.”

Bergholz noted that ready to eat products typically have very low levels of contamination with L. monocytogenes, and that the bacterium must be able to grow on the product during refrigerated storage in order to reach an infectious dose. “In many cases, the addition of organic acids will slow or stop the growth of this pathogen on ready to eat meats and seafood.”

The sometimes fatal listeriosis primarily affects older adults, pregnant women, newborns, and people with compromised immune systems, according to the Centers for Disease Control and Prevention, which offers advice for prevention here.