Whole-Genome Sequencing Characterization of Virulence Profiles of Listeria monocytogenes Food and Human Isolates and In Vitro Adhesion/Invasion Assessment

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.

Characterisation of Listeria monocytogenes Isolates from Hunted Game and Game Meat from Finland

“…LIP-I is composed of important virulence genes (including act A, hly, mpl , plc A, plc B, prf A and orf X) and is necessary for intracellular survival and spread from cell to cell [ 35 ]. LPI-1 is typically present in all L. monocytogenes strains [ 2 , 41 ]. This actA -negative deer carcass isolate (with VP3b, SG IIa and ST412) also missed the lap B (coding for an adhesion protein) and vip (coding for an invasion protein) genes, indicating a reduced virulence in this isolate.…”

“…How the absence of these two genes affects the virulence of L. monocytogenes IVb isolates needs to be further studied. Typically, ST1 (CC1) and ST4 (CC4) have been associated with clinical cases more often than other STs [ 35 , 41 ].…”

Genetic Diversity and Potential Virulence of Listeria monocytogenes Isolates Originating from Polish Artisanal Cheeses

“…Listeria monocytogenes strains may carry the llsA , llsB , llsD , llsG , llsH , llsP , llsX, and llsY genes, together designated LIPI-3 [ 5 ]. Pathogenicity studies in murine models indicated that LIPI-3 was responsible for the increased virulence of some strains of the pathogen [ 41 ].…”

“…This pathogen is characterized by great genetic diversity and variability in virulence potential [ 5 ]. Consequently, L. monocytogenes isolates originating from food belong to different molecular groups, evolutionary lineages, sequence types (ST), and clonal complexes (CC) [ 6 , 7 , 8 , 9 ].…”

“…Due to differences in the virulence potential of L. monocytogenes , not all strains are equally capable of causing human infection. Many virulence factors participate in the pathogenicity of L. monocytogenes and allow it to infect, survive in, and replicate in a variety of host cell types [ 5 ]. Subgroups of this pathogen have different virulence phenotypes that may be associated with niche specificity [ 9 ].…”