The Discovery of Five Novel Listeria Species

Five new Listeria species have been described through a collaborative project between Cornell University and Mérieux NutriSciences. Three of these species have been classified into the  Listeria sensu stricto clade, which includes the well-known food pathogen Listeria monocytogenes (LM) and the species showing close similarity to LM. The non-LM sensu stricto species (L. innocua, L. ivanovii, L. seeligeri, L. welshimeri) play a relevant role in public health as they are good indicators or even index organisms of LM contamination.

A Technical Backstory

Before this project, most of the recently described species (14/15) were so divergent from LM that they were not considered relevant by industry. However, with this discovery, there are three additions to the LM indicator set of Listeria (L. cossartiae, L. farberi, and L. immobilis) based on their phenotypic and genetic resemblance to L. marthii, L. innocua, and L. ivanovii. This is the first time since 2010 a newly described species has been added to the sensu stricto clade.

What Does All of That Mean?

Three of the recently described species can be grouped with traditional indicators for potential Listeria monocytogenes contamination. None of these new species are pathogenic or harbor any sanitizer-resistance genes. However, given that classical confirmation methods (e.g., FDA BAM, Health Canada, ISO, USDA MLG) do not describe these species, combined with the fact rapid methods have not been verified for their inclusivity, there is potential for a false negative or misclassification as a false positive. 

The Key Benefits of This Discovery to the Industry Include:

1. The food industry can improve cultural detection and rapid method-cultural confirmation agreement
2. Manufacturer of Listeria spp. Rapid methods can verify the sensitivity of their assay for “all species.”  
3. Expanding the indicator group for L. monocytogenes will improve the industry’s ability to seek and destroy growth niches, thereby improving public health.

How Is Mérieux NutriSciences  Addressing This Discovery?

Confirmation procedures are being updated to address possible misclassification and prevent false negatives. Inclusivity experiments are being performed to verify the recently described species will be detected by the Listeria spp—rapid methods used by Mérieux NutriSciences.