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New Delhi metallo-β-lactamase 1 (NDM-1) is an Ambler class B β-lactamase enzyme named after the capital of India, New Delhi. This class of enzymes requires Zn2+ ions for activity, hence metallo-β-lactamase. The transmissible genetic element–associated blaNDM-1 encodes NDM-1, which confers resistance to all β-lactam antibiotics except monobactams. The gene was first identified and reported in 2009 from a urinary tract infection–causing carbapenem-resistant Klebsiella pneumoniae isolate. Reportedly, the blaNDM-1–harboring K. pneumoniae strain (linked to sequence type 14) was isolated from an India-born patient in Sweden who acquired a urinary tract infection while visiting New Delhi.
NDM’s eponymous association with New Delhi sparked anguish among authorities in India, who saw the terminology as a means to tarnish the country’s growing medical tourism industry. Some suggested changing the term to PCM (plasmid-encoding carbapenem-resistant metallo-β-lactamase). However, the sporadic concerns regarding nomenclature were never formally addressed, and the term NDM-1 eventually gained universal acceptance within the scientific community. By the end of 2025, >63 distinct NDM variants had been reported worldwide and sequentially designated NDM-1 through NDM-63.