Soil Collected from a Single Great Smoky Mountains Trail Contains a Diversity of Listeria monocytogenes and Listeria spp

Taxonomy, ecology, and relevance to food safety of the genus Listeria with a particular consideration of new Listeria species described between 2010 and 2022

Since 2010, the genus Listeria has had the addition of 22 new species that more than tripled the number of species identified until 2010. Sixteen of these 22 new species are distantly related to the type species, Listeria monocytogenes, and several of these present phenotypes that distinguish them from classical Listeria species (L. monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, Listeria welshimeri, and Listeria grayi). These 22 newly described species also show that Listeria is more genetically diverse than previously estimated. While future studies and surveys are needed to clarify the distribution of these species, at least some of these species may not be widely spread, while other species may be frequently found spread to human-related settings (e.g., farms and processing facilities), and others may be adapted to specific environmental habitats. Here, we review the taxonomic, phylogenetic, and ecological characteristics of these new Listeria species identified since 2010 and re-iterate the suggestion of re-classification of some species into three new genera: Murraya, Mesolisteria, and Paenilisteria. We also provide a review of current detection issues and the relevance to food safety related to the identification of these new species. For example, several new non-pathogenic species could be misidentified as the pathogen L. monocytogenes, based on methods that do not target L. monocytogenes-specific virulence genes/factors, leading to unnecessary product recalls. Moreover, eight species in the proposed new genus Mesolisteria are not good indicators of environmental conditions that could allow L. monocytogenes to grow since Mesolisteria species are unable to grow at low temperatures.