Characterization of Globally Spread Escherichia coli ST131 Isolates

The characterization of a broad representative sample of ST131 Escherichia coli isolates from different origins and settings (1991 to 2010) revealed that this clonal group has likely diversified recently and that the expansion of particular variants has probably been favored by the capture of diverse, multidrug-resistant IncFII plasmids (pC15-1a, pEK499, pKF3-140-like). The low ability to adhere and to grow as biofilm that was detected in this study suggests unknownmechanisms for the persistence of this clonal group which need to be further explored. The B2-ST131 Escherichia coli clone is currently spread world-wide among humans, but it is also being frequently recovered from livestock and companion animals (28, 29). Variants showing highly similar pulsed-field gel electrophoresis (PFGE) types but variable content of antibiotic resistance and virulence genes seem to be locally amplified in different areas (1, 4, 7, 22, 33). The acquisition of a diversity of genes encoding extended-spectru