Systematic surveillance of Carbapenemase-producing Enterobacterales reveals persistent spread of IMP-4 IncM2 plasmids in New Caledonia

Carbapenemase-producing Enterobacterales (CPE) have been designated by the World Health Organization as critical global priority pathogens. Their widespread dissemination and nosocomial outbreaks pose a major public health threat. This study examined the transmission patterns and genetic characteristics of CPE isolated in New Caledonia between 2013 and 2022. A total of 214 CPE isolates were collected, comprising 199 non-duplicate clinical isolates from 164 patients and 15 environmental isolates from hospital surfaces. Isolates were characterized using phenotypic methods and whole-genome sequencing. Among clinical isolates, the most prevalent genera was Enterobacter (n = 68; 34%) and Klebsiella (n = 50; 25%), with 194 isolates (98%) harbouring IMP-type carbapenemases. WGS of 89 selected CPE revealed the predominance of the blaIMP-4 gene (n = 82; 92%). This gene was primarily associated with IncM2-type plasmids carrying a class 1 integron, identified in 65 sequenced isolates. Long-read sequencing resolved these plasmids into seven distinct variants, differentiated by integron structures and a 9305-bp insertion. Genomic, phenotypic, and epidemiological triangulation have identified 12 hospital spread events, with 10 linked to IMP-4 IncM2 plasmids, whose transferability is confirmed by conjugation assays. These results highlighted the pivotal role of plasmid-mediated dissemination in CPE spread and emphasize the urgency of enhanced surveillance to curb silent transmission. The study provided critical insights for targeted infection control strategies in New Caledonia healthcare system, with broader implications for regional antimicrobial resistance containment. Certain bacteria that resist antibiotics, known as Carbapenemase-Producing Enterobacterales (CPE), are becoming more common worldwide and are harder to treat. This study examined how these bacteria spread in hospitals in New Caledonia from 2013 to 2022. Most carried a resistance gene called blaIMP-4, often found on a small piece of DNA that can move between bacteria. This means the resistance can spread easily between different types of bacteria. The researchers identified 12 hospital spread events, mainly caused by this gene moving between bacteria rather than a single strain spreading. These findings highlight the need for better monitoring and infection control to prevent the hidden spread of antibiotic resistance. Bourles et al., analyse Carbapenemase-producing Enterobacterales isolates from human and hospital environments in New Caledonia using phenotypic methods and whole-genome sequencing. They found widespread IMP-4 driven, plasmid-mediated transmission, with IncM2 plasmids underpinning most outbreaks and facilitating ongoing spread.