Figure 3

Minimum spanning tree based on allelic profiles by using BioNumerics version 4.6. (Applied-Maths, Sint-Martens-Latem, Belgium). The comparative set included 656 L. monocytogenes strains from the French Reference Centre for Listeria and the WHO Collaborative Centre for Foodborne Listeriosis. The experimental set included 92 L. monocytogenes strains defined as virulent (“virulent to mice”) or low-virulence (phenotypic Groups “I to VI”) using a virulence test combining a PF assay in HT-29 cells and sub-cutaneous inoculation of mice. Each circle corresponds to a sequence type (ST). ST numbers are given inside the circles. The lines between STs show inferred phylogenetic relationships and are represented by bold, continuous, dotted and pale dotted lines according to the number of allelic mismatches between profiles (1, 2, 3 and 4 or more, respectively); the discontinuous links are only indicative, as alternative links of equal weight may exist. Phenotypic Groups (I to VI) of low-virulence and virulent L. monocytogenes strains are marked in color. The comparative set of L. monocytogenes strains are in white. Specific STs for Groups-Ia, -Ib and -IIIa and A23 strains are in an area shaded grey.