blaCTX-M-1/9/1 Hybrid Genes May Have Been Generated from blaCTX-M-15 on an IncI2 Plasmid.

Three hybrid CTX-M β-lactamases, CTX-M-64, CTX-M-123, and CTX-M-132, with N and C termini matching CTX-M-1 group enzymes and centers matching CTX-M-9 group enzymes, have been identified. The hybrid gene sequences suggested recombination between blaCTX-M-15 and blaCTX-M-14, the two most common blaCTX-M variants worldwide. However, blaCTX-M-64 and blaCTX-M-123 are found in an ISEcp1-blaCTX-M transposition unit with a 45-bp "spacer," rather than the 48 bp usually associated with blaCTX-M-15, and 112 bp of IncA/C plasmid backbone. This is closer to the context of blaCTX-M-55, which has one nucleotide difference from blaCTX-M-15, on IncI2 plasmid pHN1122-1. Here, we characterized an IncI2 plasmid carrying blaCTX-M-15 with a 45-bp spacer (pHNY2-1) by complete sequencing and also sequenced IncI2 plasmids carrying blaCTX-M-64 (pHNAH46-1) or blaCTX-M-132 (pHNLDH19) and an IncI1 plasmid carrying blaCTX-M-123 (pHNAH4-1). pHNY2-1 has the same ISEcp1-blaCTX-M-IncA/C insertion as pHN1122-1, pHNAH46-1, and pHNLDH19, and all four plasmid backbones are almost identical. pHNAH4-1 (IncI1 sequence type 108 [ST108]) carries a transposition unit that includes a 2,720-bp fragment of the IncI2 backbone, suggesting ISEcp1-mediated transfer of blaCTX-M-IncA/C-IncI2 to an IncI1 plasmid. All three hybrid blaCTX-M genes may have resulted from recombination between blaCTX-M-14 and blaCTX-M-15 with a 45-bp spacer on an IncI2 plasmid. Five additional Escherichia coli isolates of different sequence types from different provinces, farms, and/or animals had blaCTX-M-64 on a pHNAH46-1-like IncI2 plasmid and 9 had blaCTX-M-123 on a pHNAH4-1-like IncI1 ST108 plasmid. Thus, epidemic IncI plasmids may be responsible for the spread of blaCTX-M-64 and blaCTX-M-123 between different animals and different locations in China.