Small-Scale Comparative Genomic Analysis of Listeria monocytogenes Isolated from Environments of Salmon Processing Plants and Human Cases in Norway

Trond Løvdal,Bjørn Roth,Arvind Y M Sundaram,Lin T Brandal,Bjørn Tore Lunestad,Umaer Naseer

doi:10.3390/hygiene1010005

Abstract

Listeria monocytogenes is a food-borne bacterium that give rise to the potentially life-threatening disease listeriosis. Listeriosis has been mandatorily notifiable in Norway since 1991. All clinical L. monocytogenes isolates are sent to the Norwegian Institute of Public Health (NIPH) for typing. Since 2005 Multi-Locus Variable number tandem repeats Analysis (MLVA) has been used for typing but was recently replaced by whole genome sequencing using core genome Multi-Locus Sequence Typing (cgMLST). In the present study, L. monocytogenes isolates collected at salmon processing plants in Norway in 2007 (n = 12) and 2015 (n = 14) were first subject to MLVA. Twelve clinical L. monocytogenes isolates with matching MLVA profile and sampling time were selected from the strain collection at NIPH. Twenty-one isolates from the salmon processing plants and all clinical isolates (n = 12) were whole genome sequenced and compared using cgMLST and in silico detection of virulence genes. cgMLST revealed four pairs of environmental–human isolates with ≤10 allelic differences over 1708 genes, indicating that they may be assigned as clonal, with the implication that they are descended from the same recent ancestor. No relevant difference in carriage of virulence genes was found between environmental or human isolates. The present study shows that L. monocytogenes strains that genetically resemble contemporary isolates from human listeriosis circulate in Norwegian salmon slaughterhouses, and carry the same virulence genes.

Highlights

IntroductionListeria monocytogenes is a food-borne pathogen that can cause listeriosis, a severe invasive infection in humans with high lethality (25%–30%) and hospitalization (>92%) rates [1]
The main objective of the present study was to compare L. monocytogenes isolates collected from Norwegian salmon slaughterhouses, with L. monocytogenes isolates from human cases with the use of whole genome sequencing (WGS), in order to explore the existing L. monocytogenes strains in slaughterhouse environments and their possible association with disease in humans
No L. monocytogenes was found in plant A, but a total of 7 isolates of L. monocytogenes was found at plant B–D, and an additional 7 isolates from plant D isolated during a three-week period in October/November 2015 were acquired from an external laboratory

Summary

Introduction

Listeria monocytogenes is a food-borne pathogen that can cause listeriosis, a severe invasive infection in humans with high lethality (25%–30%) and hospitalization (>92%) rates [1]. It has been estimated that listeriosis resulted in 23,150 illnesses, 5463 deaths and 172,823 disability-adjusted life-years globally in 2010 [2]. A global trend of increasing sporadic listeriosis cases was observed at the beginning of the new millennium, especially in the age group >60 [3,4,5,6], but over the 5-year period during 2015–2019, the trend has been flat after a long period of increase [7]. In addition to the elderly, individuals with impaired immune systems, pregnant women, and new-borns are predisposed to listeriosis [8,9].

Objectives

Methods

Results

Discussion

Conclusion