Evidence of structural rearrangements and variability in pESI(like) megaplasmids of S.Infantis by resolving the pESI-like-blaCTX-M-1 positive variant

The increasing prevalence of pESI(like)-positive, multidrug-resistant (MDR) S. Infantis in Europe is a cause of major concern. As previously demonstrated, the pESI(like) megaplasmid is not only a carrier of antimicrobial resistant (AMR) genes (at least tet, dfr and sul genes), but also harbours several virulence factors and toxin/antitoxin systems that enhance its persistence in the S. Infantis host. In this study, five pESI(like) plasmids were long-read sequenced using Oxford Nanopore Technology (ONT) and their complete sequences were resolved. Comparison of the structure and gene content of the five sequenced plasmids, and further comparison with previously published pESI(like) sequences, indicated that although the sequence of pESI(like) remains almost identical, its structure is composed of regions inserted or transposed after different events. The results obtained in this study are essential to better understand the plasticity and the evolution of the pESI(like) megaplasmid, and therefore to better address risk management options and policy decisions to fight against AMR and MDR in Salmonella and other food-borne pathogens.