ISEcp1-mediated transposition of linked bla _CTX-M-3 and bla _TEM-1B from the IncI1 plasmid pEK204 found in clinical isolates of Escherichia coli from Belfast, UK

Objectives: Linked bla _CTX-M-3-bla _TEM-1b genes, as found on the IncI1 plasmid pEK204 prevalent in Belfast, also occur on plasmids belonging to other rep types in Escherichia coli isolated from nursing-home residents in Belfast. We investigated the mechanisms for their joint dissemination among diverse plasmids. Methods: Plasmid pEK204 was transferred by electroporation into E. coli DH5α harbouring derivative pBAD Myc-His vectors. Transposition experiments were then performed at 37°C. Transposition of bla genes onto the derivative pBAD Myc-His vector was confirmed by sequencing. Results: ISEcp1 mediated transposition of bla _CTX-M-3 alone from pEK204, as well as both bla _CTX-M-3 and bla _TEM-1b jointly. The 5' and 3' termini of the transposed fragments were identical to or resembled the ISEcp1 IR _L and IR _R, respectively, thereby replicating the environments previously found in various Belfast clinical plasmids harbouring bla _CTX-M-3. Conclusions: Simultaneous dissemination of bla _CTX-M-3 and bla _TEM-1b among plasmids in Belfast's nursing homes is facilitated by ISEcp1-mediated transposition of these bla genes from pEK204-like and other plasmids. Such transposition events are of public health concern, as they potentially allow wider dissemination of CTX-M-3 enzyme than would be possible through the spread of extended-spectrum β-lactamase-encoding plasmids and strains alone.