b. The ratio of rates at which recombination and mutation occur, representing a measure of how often recombination events happen relative to mutations. The phylogram based on the analysis with correction for recombination revealed that the time to the most recent common ancestor (TMRCA) of L. innocua subgroups A and B was similar (Figure 3), suggesting that these two subgroups appeared at approximately the same time. In addition, our study also showed the TMRCA of L. monocytogenes lineages I and II were similar, consistent with a recent report [24]. Figure 3 A 95% majority-rule consensus tree based on ClonalFrame

output with correction for recombination. The X-axis represents the estimated time to the most recent common ancestors (TMRCA) of the L. innocua-L. monocytogenes clade. Blue dash line shows the estimated time to the most recent common ancestors

of L. innocua subgroups I and II. Distribution of L. innocua isolates among different ABT-737 order sources Of the 29 L. innocua food isolates, 13 were obtained from meat, 8 from milk and 8 from seafoods. The majority of meat isolates (10/13, 76.9%) belonged to subgroup A, while most seafood isolates (5/8, 62.5%) belonged to subgroup B. There were significant associations between subgroups and source of isolation (p < 0.05). L. innocua isolates lack virulence genes found in L. monocytogenes, and were nonpathogenic to mice All L. innocua strains lacked 17 virulence 4EGI-1 genes examined, with the exception of the subgroup D strain (L43) harboring inlJ (87.5%-93.6% nucleotide identities to L. monocytogenes reference strains EGDe and F2365) and two subgroup B strains (1603 and 386) bearing bsh (97.7%-99.4% nucleotide identities to EGDe and F2365). All of these L. innocua strains were Glycogen branching enzyme nonpathogenic to ICR mice (Table 1). Discussion The ecological, biochemical and genetical resemblance as well as the clear differences of virulence between L. monocytogenes and L. innocua make this bacterial clade

attractive as models to examine the evolution of pathogenicity in Listeria genus. L. monocytogenes causes life-threatening infections in animals and human populations, and exhibits a diversity of strains with different pathogenicity [25]. L. innocua has once been postulated as the nonpathogenic variant of L. monocytogenes, and holds the key to understanding the evolutionary history of the L. monocytogenes-L. innocua clade. However, information on the Daporinad concentration phylogenetic structure and microevolution of L. innocua is still lacking. Thus, we characterized L. innocua strains in our laboratory stock from phylogentic perspectives. Profiling of 37 internalin genes grouped the L. innocua strains into five internalin types, IT1 to IT5, with IT1 and IT2 as the major types (Table 2). The MLST scheme identified two major phylogenetic branches containing the majority of sequence types (29/31, 93.5%), and other two bearing one strain each (Fig 1). Consequently, L.