title: Polyphasic characterization and genetic relatedness of low-virulence and virulent Listeria monocytogenes isolates.
abstract: BACKGROUND
  Currently, food regulatory authorities consider all Listeria monocytogenes isolates as equally virulent. However, an increasing number of studies demonstrate extensive variations in virulence and pathogenicity of L. monocytogenes strains. Up to now, there is no comprehensive overview of the population genetic structure of L. monocytogenes 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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Loss of virulence in lineage II strains was related to point mutation in a few virulence genes (prfA, inlA, inlB, plcA). 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 prfA or inlA.
authors.affiliation: INRA, UR 1282 Infectiologie Animale et Santé Publique, Agents transmissibles et Infectiologie, F-37380, Nouzilly and IFR, 136, France. sylvie.roche@tours.inra.fr
authors.forename: Sylvie M
authors.initials: SM
authors.lastname: Roche
authors.forename: Olivier
authors.initials: O
authors.lastname: Grépinet
authors.forename: Annaëlle
authors.initials: A
authors.lastname: Kerouanton
authors.forename: Marie
authors.initials: M
authors.lastname: Ragon
authors.forename: Alexandre
authors.initials: A
authors.lastname: Leclercq
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Témoin
authors.forename: Brigitte
authors.initials: B
authors.lastname: Schaeffer
authors.forename: Gilbert
authors.initials: G
authors.lastname: Skorski
authors.forename: Laurent
authors.initials: L
authors.lastname: Mereghetti
authors.forename: Alban
authors.initials: A
authors.lastname: Le Monnier
authors.forename: Philippe
authors.initials: P
authors.lastname: Velge
mesh_terms: D000818:Animals; D016000:Cluster Analysis; D004195:Disease Models, Animal; D016521:Electrophoresis, Gel, Pulsed-Field; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D008089:Listeria monocytogenes / Q000145:classification* / Q000302:isolation & purification / Q000472:pathogenicity*; D051379:Mice; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D017422:Sequence Analysis, DNA; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D037521:Virulence Factors