In the lineage I, the phenotypic Groups-IV, -V and -VI did not form specific clusters but were mixed with virulent strains (Figure 1). This is probably related to the absence of a genotypic Group and probably corresponds to multiple genomic backgrounds. No low-virulence strain was found in lineage III/IV, but the small number of strains in this lineage hampered us to conclude in the

rate of low-virulence strains. Sequencing of virulence and housekeeping genes To investigate the population structure and diversity of the low-virulence strains compared to virulent strains, three virulence genes were sequenced (prfA, inlA and actA) R788 molecular weight as well as seven housekeeping genes (acbZ, bglA, cat, dapE, dat, ldh, and lhkA). The dendrograms of the concatenated nucleotide sequences of virulence and housekeeping genes performed with the NJ method were presented Figure 2A and 2B, respectively. They showed different relationships among lineages and in part for some lineage I low-virulence strains. In the housekeeping-gene tree, lineage III/IV strains formed a sister group to lineage I isolates as previously click here selleck chemical described [16]. However, as also observed by Tsai et al.[16], this was not the case with the virulence-gene tree where the strains of serotype 4a and 4c formed different branches. In the same

way, all strains of serotype 4b were on the same branch in the housekeeping-gene tree. That was not the case in the virulence-gene tree where

few strains of serotype 4b Cell press were on the same branch as strains of serotype 1/2b and 3b. Similar variations were observed for strains of serotype 1/2a which were on the same branch in the housekeeping-gene tree, whereas with the virulence-gene tree, 7 strains were on different branches than the other 34 serotype 1/2a strains (bootstrap 100%). This observation comforted the hypothesis that numerous recombinations have occurred with the virulence genes. Figure 2 A Dendrogram of the prfA , actA and inlA gene sequencing using the NJ method with BioNumerics v.4.6 software showing the genetic relationships between 92  L. monocytogenes strains. The tree was constructed on the basis of the mean matrix distances of the three virulence genes. The low-virulence strains are in red. Phenotypic groups were based on results of cellular entry, plaque formation, and the two phospholipase C activities. Genotypic groups were defined as follows: Group-Ib included the strains with PrfAK220T, Group-Ia included the strains with PrfAΔ174-237, and Group-IIIa had the same mutations in the plcA, inlA and inlB genes. Group-Ic showed the K130Q mutation. B. MLST-based dendrogram using the NJ method with BioNumerics v4.6 software showing the genetic relationships between 92 L. monocytogenes strains. The tree was constructed on the basis of the mean matrix distances of seven housekeeping genes (acbZ, bglA, cat, dapE, dat, ldh, and lhkA). The low-virulence strains are in red.