Characterization of IncF plasmids carrying the bla_CTX-M-14 gene in clinical isolates of Escherichia coli from Korea

Objectives: The purpose of this study was to investigate the molecular epidemiology of CTX-M-14-producing Escherichia coli clinical isolates from Korea. Methods: A total of 138 non-duplicate E. coli clinical isolates showing reduced susceptibility or resistance to ceftazidime and/or cefotaxime were included in the study. Resistance genes, genetic environment, R plasmid size and replicon type, sequence type (ST) and XbaI-macrorestriction patterns were determined. Results: Among 138 isolates, 35 were found to carry the bla_CTX-M-14 gene. The ISEcp1 element was identified in the upstream region of the bla_CTX-M-14 gene in 32 isolates. The bla_CTX-M-14 gene was located on an IncF plasmid in 21 isolates, on an IncA/C plasmid in 1 isolate, on the chromosome in 8 isolates and on both the chromosome and an IncF plasmid in 5 isolates. The most prevalent ST was ST405 (n=8), followed by ST354 (n=4), ST38 (n=3), ST69 (n=3) and the intercontinental ST, ST131 (n=3). PFGE and multilocus sequence typing experiments demonstrated no major clonal relationship among the CTX-M-14-producing isolates. Conclusions: The bla_CTX-M-14 gene was probably mobilized by IncF plasmids, which can readily spread in E. coli, causing horizontal dissemination of the resistance gene in Korea.