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

ABSTRACT 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. IMPORTANCE The horizontal gene transfer events are the major contributors to the current spread of CTX-M-encoding genes, the most common extended-spectrum β-lactamase (ESBL), and many clinically crucial antimicrobial resistance (AMR) genes. This study presents evidence of the critical role of IS26 transposable element for the mobility of bla CTX-M gene among Escherichia coli isolates from children and domestic animals in the community. We suggest that the nucleotide sequences of IS26-bla CTX-M could be used to study bla CTX-M transmission between humans, domestic animals, and the environment, because understanding of the dissemination patterns of AMR genes is critical to implement effective measures to slow down the dissemination of these clinically important genes.