Plasmid genomic epidemiology of bla NDM carbapenemase-producing Enterobacterales in Canada from 2010 to 2023

Carbapenems are broad-spectrum antibiotics that are losing effectiveness against infections caused by multidrug-resistant Enterobacterales that have acquired carbapenemase genes. The New Delhi metallo- β -lactamase ( bla NDM ) is one of the most common carbapenemases in Canada and around the globe. These genes are frequently found on conjugative plasmids, which can disseminate through horizontal gene transfer. We applied whole-genome sequencing to characterize 1,032 bla NDM carbapenemase-producing Enterobacterales isolates collected by the Canadian Nosocomial Infection Surveillance Program from 2010 to 2023. Using a combination of short-read and long-read sequencing, we obtained 226 complete and circular bla NDM -encoding plasmids. Unlike other carbapenemases in Canada, we found that bla NDM plasmids were very diverse; there was a lack of dominant clusters identified using MOB-suite, and clustering methods were not able to accurately predict plasmid clusters for short-read-only data. The majority of bla NDM plasmids were IncF-type (69.0%, 156/226). Both bla NDM and bla OXA-48-type carbapenemase genes were found in 11.4% (118/1,032) of isolates, and we identified several instances of both carbapenemase genes co-harboured on the same plasmid replicon ( n =9). Our findings highlight that plasmid transfer has not played a major role in bla NDM transmission across Canada and that long-read sequencing is essential for resolving bla NDM plasmid structure and cluster membership.