Virulence potential of Listeria monocytogenes strains recovered from pigs in Spain
Abstract
Background: Listeria monocytogenes is a foodborne bacterial pathogen that causes listeriosis, an infectious disease of animals and humans, with pigs acting as asymptomatic reservoirs. In August 2019 a listeriosis outbreak associated with the consumption of pork meat caused 222 human cases in Spain. Determining the diversity as well as the virulence potential of strains from pig origin is important for public health concerns. Methods: The behavior of twenty-three L. monocytogenes strains recovered from pig tonsils, meat and skin was compared by studying: (1) Internalin A (InlA), Internalin B (InlB), Listeriolysin O (LLO), Actin assembly-inducing protein (ActA) and PrfA expression levels, and (2) invasion and intracellular growth in eukaryotic cells. Results: Marked differences were found in the expression of the selected virulence factors and the invasion and intracellular replication phenotypes of the L. monocytogenes strains. Strains obtained from meat samples and belonging to ST 1/2a did not have InlA anchored to the peptidoglycan. Some strains expressed higher levels of the studied virulence factors and invaded and replicated intracellularly more efficiently than an epidemic L. monocytogenes reference strain (F2365). Conclusion: This study demonstrates the presence of virulent L. monocytogenes strains in pigs, with valuable implications in veterinary medicine and food safety.
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