IS26 mediated blaCTX-M-65 amplification in Escherichia coli increase the antibiotic resistance to cephalosporin in vivo

Objectives: To characterize two Escherichia coli strains isolated from a patient pre-and post-treatment, using ,B-lactams and ,B-lactam/ ,B-lactamase inhibitor combinations (BLBLIs).Methods: A combination of antibiotic susceptibility testing (AST) with whole genome sequencing using Illumina and Oxford Nanopore platforms. Long-read sequencing and reverse transcription-quantitative PCR were performed to determine the copy numbers and expression levels of antibiotic resistance genes (ARGs), respectively. Effect on fitness costs were assessed by growth rate determination.Results: The strain obtained from the patient after the antibiotic treatment (XH989) exhibited higher resistance to cefepime, BLBLIs and quinolones compared with the pre-treatment strain (XH987). Sequencing revealed IS26-mediated duplications of a IS26 -fosA3 -blaCTX-M-65 plasmid-embedded element in strain XH989. Long-read sequencing (7.4 G data volume) indicated a variation in copy numbers of blaCTX-M-65 within one single culture of strain XH989. Increased copy numbers of the IS26 -fosA3- blaCTX-M-65 element were correlated with higher CTX-M-65 expression level and did not impose fitness costs, while facilitating faster growth under high antibiotic concentrations.Conclusion: Our study is an example from the clinic how BLBLIs and ,B-lactams exposure in vivo possibly promoted the amplification of an IS26-multiple drug resistance (MDR) region. The observation of a copy number variation seen with the blaCTX-M-65 gene in the plasmid of the post-treatment strain expands our knowledge of insertion sequence dynamics and evolution during treatment.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )