Multifacility cluster of mcr-9 and blaNDM-1 Citrobacter freundii complex and Enterobacter cloacae complex from enironmental and human reservoirs

A total of 20 isolates from the Citrobacter freundii complex and the Enterobacter cloacae complex (ECC) retrieved from diverse clinical samples collected across three healthcare facilities in southern Ireland were analyzed for harboring both blaNDM-1 and mcr-9.1 genes. Phenotypic testing revealed greater resistance potential of C. freundii isolates to tested antimicrobials (except amikacin and aztreonam) compared to ECC. Predicted plasmid analysis identified 17 plasmid replicon types, with IncHI2A and IncHI2 being the only types present in all isolates, suggesting potential dissemination pathways for blaNDM-1 and mcr-9.1 genes. Virulence factors were largely absent in plasmidic contigs; however, one aerobactin pathogenicity cluster (iroB/C/D/E) was detected in the chromosomal contigs of a single ECC isolate. The present findings underscore the importance of ongoing surveillance and contribute to understanding patterns of colistin and carbapenemase resistance gene co-dissemination within healthcare facilities of narrow spatial distances.