Background Listeria monocytogenes is a foodborne bacterial pathogen that causes listeriosis, an infectious disease in animals and people, with pigs acting as asymptomatic reservoirs. In August 2019 an outbreak associated with the consumption of pork meat caused 222 human cases of listeriosis in Spain. Determining the diversity as well as the virulence potential of strains from pigs is important to public health.
Methods The behaviour of 23 L monocytogenes strains recovered from pig tonsils, meat and skin was compared by studying (1) internalin A, internalin B, listeriolysin O, actin assembly-inducing protein and PrfA expression levels, and (2) their 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 L monocytogenes strains. Strains obtained from meat samples and belonging to serotype 1/2a did not have internalin A 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 with virulent potential in pigs, with valuable implications in veterinary medicine and food safety.
- virulence factor
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Funding This study was supported by the Agency for Innovation and Development of Andalucía (IDEA; project reference 351504/550859), by the University of Córdoba Research Program (Spain), by the Andalusian FEDER Operational Funding Program, by Generalitat Valenciana (project reference GV/2018/A/183) and by the Spanish Ministry of Science and Innovation (project reference PID2019-110764RA-I00). JG-L is supported by a 'Ramón y Cajal' contract of the Spanish Ministry of Economy and Competitiveness (RYC-2014-16735). JJQ is supported by a 'Ramón y Cajal' contract of the Spanish Ministry of Science, Innovation and Universities (RYC-2018-024985-I). The funding bodies had no role in the design of the study, in the collection, analysis and interpretation of data, and in writing the manuscript.
Competing interests None declared.
Ethics approval This experiment and all animal procedures were performed according to the guidelines of the EU (Directive 2010/63/EU). As the data used in this study were part of a routine slaughterhouse activity, no ethical committee approval was needed.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information.
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