Emergence of CTX-M-12 extended-spectrum beta-lactamase-producing Escherichia coli in Korea.

Objectives: To characterize CTX-M-12 extended-spectrum beta-lactamase (ESBL) produced by clinical Escherichia coli isolates and to investigate its genetic environment.
Methods: Antimicrobial susceptibilities were determined by disc diffusion and agar dilution methods, and the double-disc synergy test was carried out. Detection of genes encoding class A beta-lactamases was performed by PCR amplification, and the genetic environments of the bla(CTX-M-12) genes were investigated by PCR and sequencing of the regions surrounding the genes. Kinetic parameters were determined from purified CTX-M-12.
Results: Sequence data for the CTX-M-1 cluster from three clinical E. coli isolates indicated the presence of CTX-M-12. An ISEcp1 insertion sequence was located 49 bp upstream of bla(CTX-M-12) in all three E. coli isolates. CTX-M-12 had a more potent hydrolytic activity against cefotaxime than against ceftazidime and was encoded on a self-transferable approximately 18 kbp plasmid.
Conclusions: This work shows that CTX-M-12, which confers high-level resistance to cefotaxime but not to ceftazidime, has emerged in Korea. The bla(CTX-M-12) gene was associated with an upstream ISEcp1 insertion sequence.