# Genetic and phenotypic characterization of the plasmid-encoded NDM-80 metallo-β-lactamase in Escherichia coli isolated from a pediatric patient

## TL;DR

A new antibiotic-resistant gene variant, blaNDM–80, was found in E. coli from a child in China, showing resistance to most beta-lactam antibiotics.

## Contribution

This is the first report of blaNDM–80, revealing its genetic structure and higher resistance compared to other NDM variants.

## Key findings

- E. coli with blaNDM–80 showed resistance to most beta-lactam antibiotics except aztreonam, aztreonam-avibactam, and cefiderocol.
- blaNDM–80 has unique mutations and a plasmid structure that may enhance its resistance and transmission potential.
- NDM-80 hydrolyzes certain antibiotics more effectively than NDM-1, contributing to higher resistance.

## Abstract

Carbapenem-resistant Enterobacterales (CRE) strains carrying blaNDM variants pose a significant threat to the health of infected patients worldwide.

This study isolated a carbapenem-resistant Escherichia coli (E. coli) strain carrying blaNDM–80 from a patient in an intensive care unit in China. Antimicrobial susceptibility testing, whole-genome sequencing (WGS), plasmid transformation assay, cloning experiment, and steady-state kinetic determinations were performed to investigate antimicrobial susceptibility, the characteristics of the genetic environment, the mechanism of resistance gene transmission, resistance gene function, and antibiotic hydrolysis ability.

The results indicated that E. coli carrying blaNDM–80 showed significant resistance to all β-lactam antibiotics except for aztreonam, aztreonam-avibactam, and cefiderocol. WGS analysis revealed that the strain belonged to sequence type (ST) 155 and the O4:H51 serotype. The blaNDM–80 was carried by an unconjugated plasmid, and its complete genetic structure was found to be IS5-blaNDM–80-ble-trpF-dsbD-IS26-nmuD-ISKox3. The blaNDM–80 had single amino acid substitutions such as V88L, D130N, and M154L compared to blaNDM–1, whereas it only had the D130N mutation compared to blaNDM–5. The blaNDM–80 and blaNDM–5 had similar antimicrobial resistance profiles. However, in the absence of the native promoter, the minimum inhibitory concentrations (MICs) of blaNDM–80 for imipenem, meropenem, cefepime, and cefiderocol were twice as high as those of blaNDM–1. Steady-state kinetic determinations revealed that NDM-80 likely had higher hydrolytic activity against imipenem, meropenem, cefepime, and cefiderocol than NDM-1.

This study is the first to report on the emergence of the blaNDM–80 variant, shedding light on its functional mechanism. Our findings enrich the repertoire of NDM resistance genes and highlight the need for increased surveillance of pathogens harboring blaNDM variants.