Discovery of New Listeria Species May Improve Food Testing

Cornell University researchers have reportedly identified five new species
of Listeria that they suggest could provide new insights leading to better
methods of detecting soil bacteria in food. Funded by the U.S. Department of
Agriculture, the research was part of a larger study led by scientists at Colorado
State University and Cornell to examine the distribution of foodborne
pathogens, such as Listeria, E. coli and Salmonella, in agricultural and natural
environments. Samples were taken from fields, soil, ponds, and streams in
New York, Colorado and Florida.

Noting that of the 10 previously known species of Listeria, only two are
pathogenic to humans, the researchers claim that Listeria monocytogenes is
the main cause of Listeriosis, reportedly the cause of hundreds of deaths and
illnesses each year in the United States through infected deli meats, seafood
and produce.

According to lead study author Henk den Bakker, the study findings have implications for understanding the evolution of what makes Listeria monocytogenes pathenogenic. “The most recent common ancestor [of L. monocytogenes and closely related nonpathogenic species] was a pathogen, and that makes it difficult to reconstruct the evolution of pathogenicity in Listeria,” den Bakker said. But the five newly identified species apparently add more evidence to the existence of four distinct evolutionary branches of Listeria.

“Now we see the evolutionary tree has a couple of new branches, which gives
us a nice data set to reconstruct what happened on a genomic level during
the evolutionary transition from a free living ancestor to a pathogen.” See
Cornell Chronicle, March 26, 2014.

Issue 519