Phylogenetic analysis of the six outbreak strains.

<p>A phylogenetic tree was constructed from multiple alignment of the core genome SNPs of the 6 isolates in the present study and another 4 previous isolates from GenBank, where FPR3757 USA300 was included as an outgroup. A phylogenetic tree with 1000 bootstrap resamples of the alignment data sets was generated using the neighbor-joining method in MEGA5.0 with the contribution model of "Kimura 2-parameter". Bootstrap values are indicated at the nodes. The scale bar indicates the number of substitutions per position for a unit branch length.