Triple carbapenemase-producing Klebsiella pneumoniae ST6668 resistant to novel β-lactam/β-lactamase inhibitor combinations and cefiderocol, Northern Italy, 2025.
OBJECTIVE: Klebsiella pneumoniae ST6668 has recently emerged in Northern Italy, but data on its resistance architecture remain limited. METHODS: We identified a K. pneumoniae ST6668 (KNVO1) strain co-producing NDM-1, VIM-1, and OXA-48 carbapenemases via multiple megaplasmids from an elderly hospitalized patient who experienced clinical deterioration during a prolonged period of health care exposure. RESULTS: KNVO1 showed resistance to all tested β-lactams, including novel β-lactam/β-lactamase inhibitor combinations and cefiderocol, with susceptibility retained only to colistin, gentamycin and aztreonam/avibactam. Whole-genome sequencing confirmed the ST6668. The plasmidome included two megaplasmids (pKPC-CAV1321 and IncFIB:IncHI) carrying blaVIM-1 and blaNDM-1, respectively, and an IncL plasmid harbouring blaOXA-48. SNPs-based phylogeny demonstrated genomic distance to other ST6668 strains circulating locally, suggesting an independent introduction event. CONCLUSION: The convergence of three major carbapenemase families within ST6668 highlights the capacity of this clone to accumulate complex resistance determinants via megaplasmids, posing a serious threat to infection control and antimicrobial stewardship in health care settings.