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

The rapid dissemination of extended-spectrum β-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 bla_CTX-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.