Evolution and Comparative Genomics of F33:A−:B− Plasmids Carrying bla CTX-M-55 or bla CTX-M-65 in Escherichia coli and Klebsiella pneumoniae Isolated from Animals, Food Products, and Humans in China

isolates from various sources in China. We determined and compared the complete sequences of 17 F33:A-:B- plasmids from various sources. These plasmids appear to have evolved from the same ancestor by mobile element-mediated rearrangement, acquisition, and/or loss of resistance modules and similar IncN1, IncI1, and/or IncX1 plasmid backbone segments. Our findings highlight the evolutionary potential of F33:A-:B- plasmids as efficient vectors to capture and diffuse clinically relevant resistance genes.