Abstract
Strains of the food-borne pathogen Listeria (L.) monocytogenes have diverse virulence potential. This study focused on the virulence of three outbreak strains: the CC1 strain PF49 (serovar 4b) from a cheese-associated outbreak in Switzerland, the clinical CC2 strain F80594 (serovar 4b), and strain G6006 (CC3, serovar 1/2a), responsible for a large gastroenteritis outbreak in the USA due to chocolate milk. We analysed the genomes and characterized the virulence in vitro and in vivo. Whole-genome sequencing revealed a high conservation of the major virulence genes. Minor deviations of the gene contents were found in the autolysins Ami, Auto, and IspC. Moreover, different ActA variants were present. Strain PF49 and F80594 showed prolonged survival in the liver of infected mice. Invasion and intracellular proliferation were similar for all strains, but the CC1 and CC2 strains showed increased spreading in intestinal epithelial Caco2 cells compared to strain G6006. Overall, this study revealed long-term survival of serovar 4b strains F80594 and PF49 in the liver of mice. Future work will be needed to determine the genes and molecular mechanism behind the long-term survival of L. monocytogenes strains in organs.
Highlights
The Gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a rare, but severe food-borne infection in humans and animals
Invasive L. monocytogenes infection of non-pregnant individuals typically manifests as bacteremia/septicemia or as central nervous system infection including meningitis, meningoencephalitis and with lower prevalence rhombencephalitis and brain abscess [2,3,4]
Additional to G6006, two genomes were available from strains of the milk outbreak in Illinois: FSL-R2-503 (G6054)
Summary
The Gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a rare, but severe food-borne infection in humans and animals. Listeriosis is usually restricted to a non-invasive self-limited gastroenteritis, which typically occurs 24 h after ingestion of a large inoculum of bacteria and usually lasts two days [1]. In immunocompromised individuals and elderly, an invasive and systemic infection can occur within an incubation time of 20 to 30 days with a high mortality rate of 25–30%. Pregnant women and neonates are a high-risk group. Invasive L. monocytogenes infection of non-pregnant individuals typically manifests as bacteremia/septicemia or as central nervous system infection including meningitis, meningoencephalitis and with lower prevalence rhombencephalitis and brain abscess [2,3,4]. L. monocytogenes can infect the fetus or unborn, leading to spontaneous abortion or stillbirth
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