Ultra-deep long-read sequencing detects IS-mediated gene duplications as a potential trigger to generate arrays of resistance genes and a mechanism to induce novel gene variants such as blaCTX-M-243.

We identified the novel ESBL gene blaCTX-M-243 and illustrate a dynamic system of varying blaCTX-M copy numbers. Our results highlight the constant emergence of new CTX-M family enzymes and demonstrate a potential evolutionary platform to generate novel ESBL variants and possibly other antibiotic resistance genes.