Virulence, Adherence and Invasion Characters of Listeria monocytogenes Strains Isolated from Human and Food Products

Marius Eduard Caplan, Lorena Andreea Mateescu


Abstract. Listeria monocytogenes is an opportunistic intracellular pathogen, causing serious localized and systemic infections in vertebrates. Although heterogeneity in the virulence of L. monocytogenes has been observed, a clear correlation between the level of virulence and the origin of the strain could not be established. The purpose of the present study was to investigate, by using a complex phenotypic in vitro assay, the reveal of the soluble virulence factors, as well as the expression of cell-association in 10 L. monocytogenes strains isolated from food products and 11 isolates from patients with invasive, severe listeriosis. The strains were studied for the production of enzymatic virulence factors by cultivating on media containing specific substrate for the evaluation of soluble enzymatic factors expression (pore-forming enzymes, proteases, siderophore-like production), as well as for adherence and invasion of HEp-2 cells, by Cravioto’s adapted method. The expression of the tested soluble virulence factors revealed the production of hemolysin, esculinase, and caseinase; lipase was present exclusively in strains isolated from food specimens. All tested strains (excepting two food isolates) adhered to HEp-2 cells, with a predominant diffuse-aggregative pattern, and were invasive, with modifications in the nucleus (condensations, fragmentation) and cytoplasm alterations characteristic for apoptotic cells.  The adherence assay revealed the relationship between the type of adherence of tested strains and their source of isolation, the majority of them exhibiting predominantly a mixed, diffuse-aggregative pattern.


food, invasive listeriosis, L. monocytogenes, pathogenic factors.

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