Polyphasic characterization and genetic relatedness of low-virulence and virulent <it>Listeria monocytogenes</it> isolates

<p>Abstract</p> <p>Background</p> <p>Currently, food regulatory authorities consider all <it>Listeria monocytogenes</it> isolates as equally virulent. However, an increasing number of studies demonstrate extensive variations in virulence and pathogenicity of <it>L. monocytogenes</it> strains. Up to now, there is no comprehensive overview of the population genetic structure of <it>L. monocytogenes</it> taking into account virulence level. We have previously demonstrated that different low-virulence strains exhibit the same mutations in virulence genes suggesting that they could have common evolutionary pathways. New low-virulence strains were identified and assigned to phenotypic and genotypic Groups using cluster analysis. Pulsed-field gel electrophoresis, virulence gene sequencing and multi-locus sequence typing analyses were performed to study the genetic relatedness and the population structure between the studied low-virulence isolates and virulent strains.</p> <p>Results</p> <p>These methods showed that low-virulence strains are widely distributed in the two major lineages, but some are also clustered according to their genetic mutations. These analyses showed that low-virulence strains initially grouped according to their lineage, then to their serotypes and after which, they lost their virulence suggesting a relatively recent emergence.</p> <p>Conclusions</p> <p>Loss of virulence in lineage II strains was related to point mutation in a few virulence genes (<it>prfA, inlA, inlB, plcA</it>). These strains thus form a tightly clustered, monophyletic group with limited diversity. In contrast, low-virulence strains of lineage I were more dispersed among the virulence strains and the origin of their loss of virulence has not been identified yet, even if some strains exhibited different mutations in <it>prfA</it> or <it>inlA</it>.</p>

Abstract licence: CC BY-NC-ND

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