IncN3 and IncHI2 plasmids with an In1763 integron carrying blaIMP-1 in carbapenem-resistant Enterobacterales clinical isolates from the UK

Introduction. Imipenemase (IMP) carbapenemase genes are relatively rare among Enterobacterales in the UK. Emergence in multiple hospitals, in different strains and species, prompted an investigation into their genetic context.

Aim. Our goal was to identify and describe the elements carrying blaIMP genes in a variety of Enterobacterales from five hospitals in the UK.

Methodology. Long-read nanopore sequencing was carried out on 18 IMP-positive isolates belonging to 6 species. The locations of the blaIMP genes and other associated genetic elements were identified.

Results. Ten out of 18 isolates carried blaIMP-1 on an IncN3 plasmid (52-57 kb) in an In1763 class 1 integron. These plasmids also contained genes encoding type IV secretion and conjugal transfer proteins. Five out of 18 isolates carried blaIMP-1 in the same In1763 integron in much larger IncHI2 plasmids. A further isolate carried the In1763 integron in a chromosomally located plasmid fragment. Two isolates carried blaIMP-4 in IncHI2 plasmids. The isolates included three representatives of sequence type 20 of Klebsiella pneumoniae, with one carrying a distinct plasmid from the other two.

Conclusion. Highly similar IncN3 plasmids were found in a range of Enterobacterales, mostly K. pneumoniae and the Enterobacter cloacae complex, from three of four London hospitals, with the same In1763 integron carrying blaIMP-1 also being found in IncHI2 plasmids and chromosomally. These plasmids carried multiple elements facilitating self-Transmission. Strain typing alone was not sufficient to investigate cross-infection among this set of isolates, many of which appeared to be unrelated until plasmid analysis was undertaken, and vice versa.