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 bla TEM−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 bla CTX−M−1 on an approximately 92 kb IncI1 plasmid pCTX-M-1₈8/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.
Szmolka et al. (2026) studied this question.