IS26-mediated amplification of blaOXA-1and blaCTX-M-15with concurrent outer membrane porin disruption associated with de novo carbapenem resistance in a recurrent bacteraemia cohort

William C. Shropshire, Samuel L. Aitken, Reed Pifer, Jiwoong Kim, Micah M. Bhatti, Xiqi Li, Awdhesh Kalia, Jessica Galloway-Penã, Pranoti Sahasrabhojane, Cesar A. Arias, David E. Greenberg, Blake M. Hanson, Samuel A. Shelburne

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Background: Approximately half of clinical carbapenem-resistant Enterobacterales (CRE) isolates lack carbapenem-hydrolysing enzymes and develop carbapenem resistance through alternative mechanisms. Objectives: To elucidate development of carbapenem resistance mechanisms from clonal, recurrent ESBL-positive Enterobacterales (ESBL-E) bacteraemia isolates in a vulnerable patient population. Methods: This study investigated a cohort of ESBL-E bacteraemia cases in Houston, TX, USA. Oxford Nanopore Technologies long-read and Illumina short-read sequencing data were used for comparative genomic analysis. Serial passaging experiments were performed on a set of clinical ST131 Escherichia coli isolates to recapitulate in vivo observations. Quantitative PCR (qPCR) and qRT-PCR were used to determine copy number and transcript levels of β-lactamase genes, respectively. Results: Non-carbapenemase-producing CRE (non-CP-CRE) clinical isolates emerged from an ESBL-E background through a concurrence of primarily IS26-mediated amplifications of blaOXA-1 and blaCTX-M-1 group genes coupled with porin inactivation. The discrete, modular translocatable units (TUs) that carried and amplified β-lactamase genes mobilized intracellularly from a chromosomal, IS26-bound transposon and inserted within porin genes, thereby increasing β-lactamase gene copy number and inactivating porins concurrently. The carbapenem resistance phenotype and TU-mediated β-lactamase gene amplification were recapitulated by passaging a clinical ESBL-E isolate in the presence of ertapenem. Clinical non-CP-CRE isolates had stable carbapenem resistance phenotypes in the absence of ertapenem exposure. Conclusions: These data demonstrate IS26-mediated mechanisms underlying β-lactamase gene amplification with concurrent outer membrane porin disruption driving emergence of clinical non-CP-CRE. Furthermore, these amplifications were stable in the absence of antimicrobial pressure. Long-read sequencing can be utilized to identify unique mobile genetic element mechanisms that drive antimicrobial resistance.

Original languageEnglish (US)
Pages (from-to)385-395
Number of pages11
JournalJournal of Antimicrobial Chemotherapy
Issue number2
StatePublished - Feb 1 2021

ASJC Scopus subject areas

  • Pharmacology
  • Microbiology (medical)
  • Infectious Diseases
  • Pharmacology (medical)


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