IS26 drives the dissemination of bla_CTX-M genes in an Ecuadorian community

The rapid dissemination of extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales, mainly Escherichia coli carrying bla(CTX-M) genes, is a major public health concern due to its successful spread in hospital settings as well as among humans and animals in the community. We characterized ESBL-producing E. coli isolates from children and domestic animals in semirural communities of Ecuador to assess the contribution of horizontal gene transfer of the bla(CTX-M) genes among E. coli isolates. From 20 selected E. coli isolates (from children and domestic animals) harboring bla(CTX-M )allelic variants, we identified 16 plasmids carrying bla(CTX-M-55) (n = 9), bla(CTX-M-65) (n = 5), and bla(CTX-M-27 )(n = 2), as well as four chromosomes carrying bla(CTX-M-65). The backbone structure of plasmids, including replication, maintenance, and plasmid transfer genes, and the synteny was conserved in all plasmids carrying the same bla(CTX-M) allelic variant. In all plasmids and chromosomes, the blaCTX-M genes were bracketed by two IS26 transposable elements. This study highlights the critical role of the IS26 transposable element for the current mobility of bla(CTX-M) genes among plasmids or from plasmids to chromosomes, suggesting that IS26-bla(CTX-M) brackets could be used to study bla(CTX-M) transmission between humans, domestic animals, and the environment.