Abstract
The pathogenicity of the human foodborne pathogen Listeria monocytogenes relies on virulence factors such as internalins. In 2009/2010 two L. monocytogenes strains were responsible for a serious listeriosis outbreak in Austria, Germany, and the Czech Republic. One of these clones, QOC1, which caused 14 cases including five fatalities, encodes the novel internalins inlP1, inlPq and inlP4, and the novel internalin-like protein inlP3 in the genomic region of hypervariable genetic hotspot 9 in addition to the standard set of virulence genes. The in silico prevalence study revealed that these genes rarely occur in L. monocytogenes, mainly in minor clonal complexes. To obtain first insights of the role of these genes in the pathogenicity of L. monocytogenes, we studied the gene expression under conditions mimicking the ingestion in the host. Expression of inlP1, inlP3, inlPq and inlP4 was increased under gastric stress and in intracellular bacteria grown in intestinal epithelial cells. Furthermore, colonization of the liver and the spleen was slightly, but significantly reduced 72 h post infection in an oral mouse infection model when inlP1 or inlP4 was deleted. Moreover, the impact of InlP1 and InlP3 in virulence was shown in vitro in human intestinal epithelial cells. In this study we conclusively demonstrate a potential contribution of uncommon novel internalins and an internalin-like protein to the pathogenicity of L. monocytogenes.
Highlights
Listeria monocytogenes is one of the most concerning human foodborne pathogens as it is the causative agent of listeriosis, a rare but severe disease that is associated with high mortality rates
Two L. monocytogenes strains were assigned to this outbreak: Quargel Outbreak Clone 1 (QOC1), which caused 14 cases including five fatalities and Quargel Outbreak Clone 2 (QOC2), which caused 20 cases resulting in three fatalities
InlP2 is not encoded in full length in L. monocytogenes QOC1 and Occurrence of inlP1, inlP2, inlP3, inlPq, and inlP4
Summary
Listeria monocytogenes is one of the most concerning human foodborne pathogens as it is the causative agent of listeriosis, a rare but severe disease that is associated with high mortality rates. After ingestion of contaminated food, listeriosis can manifest as a non-invasive selflimiting gastroenteritis in healthy individuals and as an invasive and systemic infection. Ready-to-eat products are at high risk of contamination with the pathogen over the course of food processing (Gandhi and Chikindas, 2007). Genome sequencing and analysis revealed that the two outbreak strains are related but distinct and did not recently evolve from a common ancestor (Rychli et al, 2014b). Both strains belong to serotype 1/2a, but to different sequence types (ST): QOC1 is assigned to ST403 and QOC2 to ST398
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