# Derivatization of pBACpAK entrapment vectors for enhanced mobile genetic element transposition detection in multidrug-resistant Escherichia coli

## TL;DR

Researchers improved a tool to detect mobile genetic elements in drug-resistant E. coli, capturing more resistance genes like Tn7824.

## Contribution

Derivatized pBACpAK vectors with increased MGE detection rates and identified a novel composite transposon Tn7824.

## Key findings

- Derivatized pBACpAK vectors captured MGEs at 10.7–73.1% rates, significantly higher than the wild-type vector (3.75%).
- The novel composite transposon Tn7824 was identified, carrying resistance genes blaOXA-181 and qnrS1.
- Long-read sequencing confirmed MGE structures and chromosomal integration events mediated by insertion sequences.

## Abstract

Aim. Antimicrobial resistance poses a critical global health threat, driven by the dissemination of resistance genes via mobile genetic elements (MGEs). This study aims to enhance the detection of MGE insertions in multidrug-resistant Escherichia coli by derivatizing the pBACpAK entrapment vector.

Methods and results. Three derivatives were constructed with additional nucleotides upstream of the cI repressor gene, based on conserved regions identified from GenBank sequences containing known IS26 and IS1 insertions. Using colony PCR, intracellular transposition screening was performed on 194 tetracycline-resistant colonies from four E. coli ESI123 strains carrying different pBACpAK constructs. The derivatives showed increased MGE capture rates (10.7–73.1 %) compared to the WT vector (3.75%), identifying multiple MGEs, including the novel composite transposon Tn7824. Tn7824 harbours the blaOXA-181 carbapenem resistance gene and the qnrS1 quinolone resistance gene, highlighting the clinical relevance of these findings. Long-read sequencing of transposants confirmed the accuracy of MGE identification and structural characterization, which also revealed chromosomal integration events of the pBACpAK derivatives mediated by flanking insertion sequences.

Conclusions. The modifications introduced in the pBACpAK derivatives could increase the detection of transposition events by alleviating spatial constraints, allowing for more robust MGE detection.