![]() Class A, C, and D enzymes contain a serine residue at the active site of the β-lactamase, while class B enzymes contain one or two zinc ions and are therefore termed MBLs. Β-Lactamases are divided into the A, B, C, and D classes based on amino acid sequence identity ( 9, – 11). NDM-positive strains have been found worldwide, representing a significant challenge for clinical management and public health ( 7, 8). NDM-positive strains cause a variety of infections that have been reported to be associated with high mortality rates ( 6). NDM-positive strains are usually resistant to most antimicrobial agents in addition to β-lactams due to the coexistence of other resistance mechanisms ( 1). Since then, NDM-1 has been found in various species of the Enterobacteriaceae, Acinetobacter, and Pseudomonas, and 24 variants of NDM have been identified. NDM-1 was first identified in a Klebsiella pneumoniae strain isolated from a Swedish patient who had been hospitalized in New Delhi, India, in 2008 ( 2). The hydrolysis of β-lactams by NDM enzymes cannot be prevented by clinically available β-lactamase inhibitors, including avibactam, clavulanate, sulbactam, and tazobactam. Carbapenems are the mainstay antimicrobial agents of choice for treating severe infections caused by many Gram-negative bacteria ( 4, 5). NDM has poor activity against amdinocillin, an extended-spectrum penicillin antibiotic of the amidinopenicillin family ( 3). New Delhi metallo-β-lactamase (NDM) is a type of metallo-β-lactamase (MBL) able to hydrolyze most β-lactams (including carbapenems) but not monobactams ( 1, 2). NDM will remain a severe challenge in health care settings, and more studies on appropriate countermeasures are required. Evidence-based guidelines on prevention and control of carbapenem-resistant Gram-negative bacteria are available, although none are specific for NDM-positive strains. Outbreaks caused by NDM-positive strains have been reported worldwide, attributable to sources such as contaminated devices. Compounds able to inhibit NDM have been found, but none have been approved for clinical use. Polymyxins combined with other agents remain the mainstream options of antimicrobial treatment. Lateral flow immunoassays specifically detect NDM, and molecular approaches remain the reference methods for detecting bla NDM. Commonly used phenotypic tests cannot specifically identify NDM. Most bla NDM-carrying plasmids belong to limited replicon types (IncX3, IncFII, or IncC). NDM-positive strains have been identified worldwide, with the highest prevalence in the Indian subcontinent, the Middle East, and the Balkans. coli, ST167, ST410, or ST617) being the most prevalent. pneumoniae, ST11, ST14, ST15, or ST147 for E. Klebsiella pneumoniae and Escherichia coli are the predominant carriers of bla NDM, with certain sequence types (STs) (for K. Twenty-four NDM variants have been identified in >60 species of 11 bacterial families, and several variants have enhanced carbapenemase activity. New Delhi metallo-β-lactamase (NDM) is a metallo-β-lactamase able to hydrolyze almost all β-lactams.
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