Healthcare-related transmission of mobile genetic elements co-carrying bla NDM and 16S rRNA methyltransferase genes in multiple Enterobacterales

Aminoglycosides are used in the treatment of serious infections with Gram-negative bacteria, especially those resistant to beta-lactams and carbapenems. 16S rRNA methyltransferases (16S-RMTase) are capable of conferring resistance to nearly all aminoglycosides. They are sometimes detected in combination with <i>bla</i> _NDM. This study describes the mobile genetic elements associated with <i>bla</i> _NDM and 16S-RMTase (co-)carriage in <i>Enterobacterales</i> from Ireland in the period 2019-2023. All isolates (<i>n</i>=58) carrying both <i>bla</i> _NDM and a 16S-RMTase gene between 2019 and 2023 were obtained from the CPE National Reference Laboratory Service. Short-read sequences were generated for all isolates, and long-read sequences were generated for a subset of isolates (<i>n</i>=27). MOB-recon was used to distinguish plasmid-derived contigs from draft assemblies. The containment distance and DCJ-indel distance were used to find clusters of related plasmids. Isolates carrying <i>bla</i> _NDM-1 were associated with <i>armA</i> (<i>n</i>=31) but also <i>rmtC</i> (<i>n</i>=6) carriage. These genes were co-localized most frequently on IncFIB/HI1B (<i>n</i>=12), IncM2 (<i>n</i>=10) and IncC (<i>n</i>=8) plasmids. Closely related plasmids were identified in multiple species (range: 2-5) and at different sites around Ireland; however, the IncM2 plasmids were largely associated with a single hospital. Isolates carrying <i>bla</i> _NDM-5 were associated with <i>rmtB1</i> (<i>n</i>=28) carriage. The majority (<i>n</i>=15) were carried on a diverse range of mosaic IncF-type plasmids. Two discrete clusters of IncM1 (<i>n</i>=3) and IncFII (<i>n</i>=4) type plasmids were also detected. The study highlights the diverse plasmids co-carrying carbapenem and aminoglycoside resistance genes in Ireland. Detection of plasmids across multiple species and hospitals suggests dissemination driven by antimicrobial selective pressure and environmental reservoirs within healthcare networks. The co-dissemination of these genes on highly mobile plasmids poses a significant public health concern and emphasizes the need for greater awareness that chains of transmission of antimicrobial resistance in the healthcare setting may involve multiple species.