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Plasmids carrying high-risk resistance mechanisms in pathogenic E. coli have gained particular attention in veterinary medicine, especially since the discovery of the colistin resistance gene, mcr-1. Here, we provide the first evidence of its emergence and describe the complete mcr-1 plasmid sequence of a multi-resistant avian pathogenic E. coli (APEC) strain from waterfowl in Hungary. Whole-genome sequencing analysis and core-genome MLST were performed to characterize the genome structure of the mcr-1 plasmid and to reveal the phylogenetic relation between the Hungarian duck strain Ec45-2020 and the internationally circulating mcr-1-positive E. coli strains from poultry and humans. Results showed that plasmid pEc45-2020-33kb displayed a high level of genome identity with mcr-1 plasmids of IncX4 type widespread among human, animal and food reservoirs of enteric bacteria of public health. The mcr-1-positive E. coli strain Ec45-2020 belongs to the ST162 genotype, considered as one of the globally disseminated zoonotic genotypes of MDR E. coli. In accordance with international findings, our results underline the importance of continuous surveillance of enteric bacteria with high-risk antimicrobial resistance genotypes, including neglected animals, such as waterfowls, as possible reservoirs for the colistin resistance gene mcr-1. [ABSTRACT FROM AUTHOR]

Rats are particularly important from an epidemiological point of view, because they are regarded as reservoirs for diverse zoonotic pathogens including enteric bacteria. This study is the first to report the emergence of Salmonella serovar Ohio in brown rats ( Rattus norvegicus ) and food-producing animals in Hungary. We first reveal the genomic diversity of the strains and their phylogenomic relationships in the context of the international collection of S . Ohio genomes. This pathogen was detected in 4.3% (4/92) of rats, captured from multiple sites in Hungary. A whole-genome-based genotype comparison of S . Ohio, Infantis, Enteritidis, and Typhimurium strains showed that 76.4% (117/153) of the virulence and antimicrobial resistance genes were conserved among these serovars, and none of the genes were specific to S . Ohio. All S . Ohio strains lacked virulence and resistance plasmids. The cgMLST phylogenomic comparison highlighted a close genetic relationship between rat and poultry strains of S . Ohio from Hungary. These strains clustered together with the international S . Ohio genomes from aquatic environments. Overall, this study contributes to our understanding of the epidemiology of Salmonella spp. in brown rats and highlights the importance of monitoring to minimize the public health risk of rodent populations. However, further research is needed to understand the route of infection and evolution of this serovar.