Plasmid-mediated quinolone resistance (PMQR) of enterobacteria encoded by qnr genes is an emerging concern in human and veterinary medicine. Here we aimed to study PMQR of porcine Escherichia coli in two large piggeries in Romania and Hungary. The studies identified PMQR E. coli strains in 34% of piglets in the Romanian farm. Clonality of six qnrS1 E. coli strains representing the Romanian pig farm was established by multilocus sequence typing (MLST), and the qnrS1 plasmids were characterized by plasmid transfer and PCR-based replicon typing. The six tested strains were assigned to three different MLST types. All proved to carry IncN plasmids, representing the first IncN-borne qnrS1 gene to be identified in E. coli from food-producing animals. DNA sequences flanking the qnrS1 gene showed ≥99% homology with the corresponding resistance region of the pINF5 plasmid from Salmonella Infantis isolated from chicken carcass and of IncN plasmids from human clinical E. coli strains. Thus, our data suggest that transfer of qnrS1 plasmids occurs between Salmonella and E. coli of animal and human origin, with pigs representing one of the potential reservoirs. Further, we report on identification and characterization of the qnrS1 gene in porcine E. coli for the first time in Europe.