Cornell researchers have found five previously unknown and novel kinds of Listeria, according to a new study in the International Journal of Systematic and Evolutionary Microbiology. The food scientists made the discovery while examining the prevalence of Listeria in agricultural soil throughout the U.S.

Researchers said that identifying these novel species will help food facilities improve food safety by identifying potential growth niches that previously may have been overlooked.

The study led to some findings among the novel species, including that one of the novel species, Listeria immobilis, lacked motility, or the ability to move. Motility had been thought to be common among Listeria species, for example, L. monocytogenes, and used as a key test in Listeria detection methods.

“This discovery effectively calls for a rewrite of the standard identification protocols issued by food safety regulators,” lead author and Cornell doctoral student in food science, Catharine R. Carlin said.

“This research increases the set of Listeria species monitored in food production environments. Expanding the knowledge base to understand the diversity of Listeria will save the commercial food world confusion and errors, as well as prevent contamination, explain false positives and thwart foodborne outbreaks.”

The researchers state that understanding the different Listeria species is important for comprehending their similarities and that this study will help the food industry get better at identifying Listeria monocytogenes and not misidentifying it as something else.

 “When you’re inspecting the environments of food processing plants or restaurants, you need to know the pathogenic listeria from the non-pathogenic species,” said co-author Martin Wiedmann, Ph.D and Cornell’s Gellert Family Professor in Food Safety.

“You need to tell the good guys from the bad guys.”  

In the study, the researchers collected soil samples from all over the United States and agricultural water samples from New York state. From the soil and water, they found 27 Listeria isolates that could not be classified to the species level, so the lab conducted whole genome sequencing tests and showed these new species formed five novel distinct clusters.

 After naming Listeria immobilis to reflect its non-motile characteristic, three of the other species were named to honor Listeria researchers:

• Listeria cossartiae for Pascale Cossart, a bacteriologist at the Pasteur Institute of Paris
• Listeria farberi for Jeff Farber, a microbiologist at the at the University of Guelph, Canada
• Listeria portnoyii for Daniel Portnoy, a microbiologist at the University of California – Berkeley

The fifth species name, Listeria rustica, was taken from the Latin word “rusticus” and signifies its rural origin. 

The Centers for Disease Control and Prevention estimate that 1,600 people get listeriosis each year, and about 260 die, with the infection being most likely to sicken pregnant women and their newborns, adults aged 65 or older, people with weakened immune systems and young children.

According to the CDC, most people with invasive listeriosis require hospital care, and about one in five people with the infection die. When listeriosis occurs during pregnancy, it can cause miscarriage, stillbirth, or newborn death. Listeriosis during pregnancy results in fetal loss in about 20 percent and newborn death in about 3 percent of cases.