Listeria monocytogenes is already a virulent species of foodborne bacteria most often found in raw milk, soft-ripened cheeses and ready-to-eat cold cuts. It is particularly tenacious and can thrive even under refrigeration.

Now researchers say some strains of Listeria monocytogenes appear to have acquired an enhanced ability to invade and infect the heart.


Less common than Salmonella or toxic E. coli, Listeria can be far more deadly. While the majority of people infected suffer gastroenteritis and recover, Listeria kills about 16 percent of those infected, according to the Centers for Disease Control and Prevention. Other estimates place the fatality rate as high as 30 percent.

The bacteria typically affect the central nervous system or the fetus during pregnancy, but the new research indicates some unique but not uncommon strains of the pathogen target the heart, and that these variants may have adapted to increase their ability to invade heart cells.

According to a study led by Nancy Freitag, a professor at the University of Illinois Chicago, once these variant Listeria infect the heart, they can replicate faster than other strains.  Freitag and colleagues reported their findings in a paper published online Wednesday in the Journal of Medical Microbiology.

Freitag, in various interviews this week, said one implication of the study may be an increased risk of serious heart disease among those who become infected with Listeria.  During an outbreak of Listeria involving one of these strains, she said medical personnel should be aware that there’s a heightened potential for cardiac infection.

The study was supported by the U.S. Public Health Service and the American Heart Association.