Complete nucleotide sequences of bla_CTX-M-harboring IncF plasmids from community-associated Escherichia coli strains in the United States

Community-associated infections due to Escherichia coli producing CTX-M-type extended-spectrum β-lactamases are increasingly recognized in the United States. The bla_CTX-M genes are frequently carried on IncF group plasmids. In this study, bla_CTX-M-15-harboring plasmids pCA14 (sequence type 131 [ST131]) and pCA28 (ST44) and bla_CTX-M-14-harboring plasmid pCA08 (ST131) were sequenced and characterized. The three plasmids were closely related to other IncFII plasmids from continents outside the United States in the conserved backbone region and multiresistance regions (MRRs). Each of the bla_CTX-M-15-carrying plasmids pCA14 and pCA28 belonged to F31:A4:B1 (FAB [FII, FIA, FIB] formula) and showed a high level of similarity (92% coverage of pCA14 and 99% to 100% nucleotide identity), suggesting a possible common origin. The bla_CTX-M-14-carrying plasmid pCA08 belonged to F2:A2:B20 and was highly similar to pKF3-140 from China (88% coverage of pCA08 and 99% to 100% nucleotide identity). All three plasmids carried multiple antimicrobial resistance genes and modules associated with virulence and biochemical pathways, which likely confer selective advantages for their host strains. The bla_CTX-M-carrying IncFIIIA-IB plasmids implicated in community-associated infections in the United States shared key structural features with those identified from other continents, underscoring the global nature of this plasmid epidemic.