Emergence of ACME-containing ST239 variants in the ST239 population. (A) Maximum clade credibility tree of the 2000 to 2010 ST239 populations based on BEAST analysis. Branches containing ACME-containing isolates are colored red. The three colored boxes in the ST239 tree represent the three main ST239 clades. (B) Skyline plot representing the effective genetic diversity of the ST239 and ST22 populations over time. The line in the grey shading represents ST239, and the line in the red shading represents ST22, with the shaded areas representing 95% confidence intervals.