Characteristics and distribution of Listeria spp., including Listeria species newly described since 2009

Abstract

The genus Listeria is currently comprised of 17 species, including 9 Listeria species newly described since 2009. Genomic and phenotypic data clearly define a distinct group of six species (Listeria sensu strictu) that share common phenotypic characteristics (e.g., ability to grow at low temperature, flagellar motility); this group includes the pathogen Listeria monocytogenes. The other 11 species (Listeria sensu lato) represent three distinct monophyletic groups, which may warrant recognition as separate genera. These three proposed genera do not contain pathogens, are non-motile (except for Listeria grayi), are able to reduce nitrate (except for Listeria floridensis), and are negative for the Voges-Proskauer test (except for L. grayi). Unlike all other Listeria species, species in the proposed new genus Mesolisteria are not able to grow below 7 °C. While most new Listeria species have only been identified in a few countries, the availability of molecular tools for rapid characterization of putative Listeria isolates will likely lead to future identification of isolates representing these new species from different sources. Identification of Listeria sensu lato isolates has not only allowed for a better understanding of the evolution of Listeria and virulence characteristics in Listeria but also has practical implications as detection of Listeria species is often used by the food industry as a marker to detect conditions that allow for presence, growth, and persistence of L. monocytogenes. This review will provide a comprehensive critical summary of our current understanding of the characteristics and distribution of the new Listeria species with a focus on Listeria sensu lato.

Keywords: Listeria; Listeria sensu lato; Listeria sensu strictu; New genus; New species.

Fig. 1

Phylogenetic tree modified from Weller et al. (2015). Maximum likelihood phylogeny based on concatenated amino acid sequences of 325 single copy genes present in all Listeria species. Values on branches represent bootstrap values (>70 %) based on 250 bootstrap replicates. Proposed new genera names are shown close to monophyletic groups. Bar, 0.1 amino acid substitutions per site

Fig. 2

Schematic of the phylogenetic history of the current genus Listeria. Circles represent extinct ancestor species. Triangles represent the current monophyletic taxa proposed here to be classified into distinct genera. Text close to branches depicts evolutionary events of gain or loss of genetic features that help define current taxa