Abstract
BackgroundListeria monocytogenes is a widespread foodborne pathogen that can cause listeriosis, a potentially fatal infection. L. monocytogenes is subdivided into four phylogenetic lineages, with the highest incidence of listeriosis occurring within lineage I followed by lineage II. Strains of L. monocytogenes differ in their phenotypic characteristics, including virulence. However, the genetic bases for these observed differences are not well understood, and current efforts to monitor L. monocytogenes in food consider all strains to be equally virulent. We use a comparative genomics approach to identify genes and single nucleotide polymorphisms (SNPs) in 174 clinical and food isolates of L. monocytogenes that potentially contribute to virulence or the capacity to adapt to food environments.ResultsNo SNPs are significantly associated with food or clinical isolates. No genes are significantly associated with food or clinical isolates from lineage I, but eight genes consisting of multiple homologues are associated with lineage II food isolates. These include three genes which encode hypothetical proteins, the cadmium resistance genes cadA and cadC, the multi-drug resistance gene ebrB, a quaternary ammonium compound resistance gene qac, and a regulatory gene. All eight genes are plasmid-borne, and most closed L. monocytogenes plasmids carry at least five of the genes (24/27). In addition, plasmids are more frequently associated with lineage II food isolates than with lineage II clinical isolates.ConclusionsWe identify eight genes that are significantly associated with food isolates in lineage II. Interestingly, the eight genes are virtually absent in lineage II outbreak isolates, are composed of homologues which show a nonrandom distribution among lineage I serotypes, and the sequences are highly conserved across 27 closed Listeria plasmids. The functions of these genes should be explored further and will contribute to our understanding of how L. monocytogenes adapts to the host and food environments. Moreover, these genes may also be useful as markers for risk assessment models of either pathogenicity or the ability to proliferate in food and the food processing environment.
Highlights
Listeria monocytogenes is a widespread foodborne pathogen that can cause listeriosis, a potentially fatal infection
Identification of virulence and stress tolerance gene clusters The core genome of 174 isolates consists of 2322 genes, the accessory genome 2381 genes, and the pan genome 4703 genes, which is in the order of prior core genome calculations for L. monocytogenes [22, 44]
The presence of pathogenicity island Pathogenicity island LIPI-3 (LIPI-3) (LIPI-3) is variable among lineage I isolates, and surprisingly, was detected in a single isolate from lineage II. It has been detected in L. innocua [64], a complete LIPI-3 has not been previously detected in lineage II L. monocytogenes isolates, a partial LIPI-3 is present in several lineage II isolates [38]
Summary
Listeria monocytogenes is a widespread foodborne pathogen that can cause listeriosis, a potentially fatal infection. Listeria monocytogenes is a facultative intracellular pathogen that causes listeriosis, a predominantly foodborne disease with high case fatality and hospitalization rates (up to 19 and 94%, respectively) [1]. L. monocytogenes is highly resilient to various stresses It can survive refrigeration temperatures of 4 °C [4], salt concentrations as high as 13.9% and pH values as low as 4.1 [5, 6]. This capacity for tolerating extreme conditions which inhibit the growth of most foodborne pathogens
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