# Antimicrobial resistance of Escherichia coli in Hungarian wild rats and characterization of a CTX-M-1 type ESBL plasmid

## TL;DR

This study finds that brown rats in Hungary carry antibiotic-resistant E. coli, including a strain with a plasmid linked to human infections, highlighting rats as potential spreaders of drug resistance.

## Contribution

The first characterization of a CTX-M-1 type ESBL plasmid in an urban rat in Hungary and its close similarity to human-derived plasmids.

## Key findings

- 25.6% of brown rats carried antimicrobial-resistant E. coli, with 8.9% showing multidrug resistance.
- A novel E. coli strain (88/Ec2) was found to carry a CTX-M-1 plasmid similar to those in human pathogens.
- The strain belongs to a new sequence type and is phylogenetically linked to human epidemic E. coli lineages.

## Abstract

This study presents a comprehensive analysis of antimicrobial resistance in E. coli from brown rats (Rattus norvegicus), focusing on the occurrence and genetic basis of resistance and characterizing an ESBL-producing E. coli strain with a fully resolved CTX-M-1 plasmid. 25.6% of 90 brown rats carried AMR E. coli strains, with 8.9% displaying multidrug resistance. The predominant resistance pattern was combined resistance to ampicillin (17.8%) and tetracycline (12%), with plasmid-associated resistance genes blaTEM−1 and tet(A)/tet(B). The study identified the first ESBL-producing E. coli strain (88/Ec2) in an urban rat in Hungary, harboring the gene blaCTX−M−1 on an approximately 92 kb IncI1 plasmid pCTX-M-1_88/Ec2. Comparative plasmid analysis showed 98% structural similarity to CTX-M-1 plasmids from human-derived pathogens. Strain 88/Ec2 was serotyped as O168:H38 and assigned to a novel sequence type, ST17982. Phylogenetically, it exhibits a central relationship to human CTX-M E. coli lineages, suggesting a shared genomic background with globally disseminated, human epidemic E. coli lineages. These findings highlight the role of urban brown rats as reservoirs and potential vectors of antimicrobial resistance within the One Health framework and advocate for enhanced surveillance of AMR in urban wildlife to better understand and mitigate the zoonotic transfer of resistance genes.

The online version contains supplementary material available at 10.1038/s41598-026-38191-6.