Abstract
Listeria monocytogenes (Lm) is the causative agent of human listeriosis. Lm strains have different virulence potential. For this reason, we preliminarily characterised via Whole-Genome Sequencing (WGS) some Lm strains for their key genomic features and virulence-associated determinants, assigning the clonal complex (CC). Moreover, the ability of the same strains to adhere to and invade human colon carcinoma cell line Caco-2, evaluating the possible correspondence with their genetic virulence profile, was also assessed. The clinical strains typed belonged to clonal complex (CC)1, CC31, and CC101 and showed a very low invasiveness. The Lm strains isolated from food were assigned to CC1, CC7, CC9, and CC121. All CC1 carried the hypervirulence pathogenicity island LIPI-3 in addition to LIPI-1. Premature stop codons in the inlA gene were found only in Lm of food origin belonging to CC9 and CC121. The presence of LIPI2_inlII was observed in all the CCs except CC1. The CC7 strain, belonging to an epidemic cluster, also carried the internalin genes inlG and inlL and showed the highest level of invasion. In contrast, the human CC31 strain lacked the lapB and vip genes and presented the lowest level of invasiveness. In Lm, the genetic determinants of hypo- or hypervirulence are not necessarily predictive of a cell adhesion and/or invasion ability in vitro. Moreover, since listeriosis results from the interplay between host and virulence features of the pathogen, even hypovirulent clones are able to cause infection in immunocompromised people.
Highlights
This article is an open access articleListeria monocytogenes (Lm) is a major foodborne pathogen causing human listeriosis, a severe disease with the highest fatality rates of all other foodborne diseases [1,2]
The ability of Lm to adhere to and invade phagocytic and nonphagocytic cells is an important aspect of its pathogenesis, which consist of multiple stages, including cell adhesion, internalisation, vacuolar escape, intracellular replication, movement by actin mobilisation, and cell-to-cell spread [8]
The Caco-2 cells grown in 6-well tissue culture plates were infected with 107 bacteria to yield a multiplicity of infection (MOI) of approximately 100 colony-forming units (CFU) per cell
Summary
Listeria monocytogenes (Lm) is a major foodborne pathogen causing human listeriosis, a severe disease with the highest fatality rates of all other foodborne diseases [1,2]. Many studies have previously reported multiple distinct mutations that lead to premature stop codons (PMSCs) in the inlA gene that cause a dysregulated expression of the internalin protein [20,21], significantly decreasing the invasion ability of the mutated strain in human epithelial cells [22] Other proteins such as fibronectin-binding protein (FbpA), Auto, and Vip are suggested to have a role in mediating Lm’s entry into the host cell [8]. The purposes of this work were to (i) identify via WGS key genomic features and virulence-associated determinants of Lm isolates, assigning the clonal complex (CC), and (ii) characterise the ability of the strains to adhere and invade human colon carcinoma cell line Caco-2, evaluating the possible correspondence with their genetic virulence profile
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