Fig. 1

Temporal and geographical distribution of strains studied. a The number of strains per year, 1945–2017. The 2008–2017 clinical isolates are represented in red- or yellow-shaded patterns (see key), whereas the older clinical isolates are in gray and the reference strains in blue. The inset shows the pie charts with the frequency of resistance phenotypes among strains from the four most represented geographic origins; the remaining ones are pooled in the right-most pie chart. b Geographic origins of strains from the three subsets