Structural studies on New Delhi Metallo-β-lactamase (NDM-2) suggest old β-lactam, penicillin to be better antibiotic for NDM-2-harbouring Acinetobacter baumanni

Acinetobacter baumannii, a Gram-negative pathogen causes nosocomial infections including pneumonia, urinary tract and respiratory infections. Carbapenem group of -lactam antibiotics are routinely used to treat A. baumannii including multidrug-resistant clinical strains. The emergence of New Delhi Metallo--lactamase (NDM-2), a new type of -lactamase and one of the major resistant determinants in A. baumannii, opened up challenges in the treatment of resistant strains. Thus, understanding the structurefunction relationship of NDM-2 with different analogues of -lactams becomes crucial. We carried out in silico studies on the interaction of various -lactams with NDM-2 and with OXA-24, a carbapenem hydrolyzing non-NDM type -lactamase. The binding affinity of the -lactams to NDM-2 was found to be in the order: ceftazidime approximate to imipenem approximate to doripenem>oxacillin>aztreonam>penicillin; however, the order of their affinity to OXA-24 was quite different: ceftazidime>aztreonam>penicillin>oxacillin>doripenem>imipenem. Further, NDM-2 in comparison to OXA-24 showed stronger interaction (less X-score) with most of the -lactams except penicillin. This suggests higher lethality posed by clinical strains expressing NDM-2 than those without NDM-2. Weak interaction between NDM-2 and penicillin clearly points out that penicillin is perhaps better option in treating A. baumannii harbouring NDM-2. Present findings provide new insights in drug resistance at the molecular level of NDM-2 and can help in designing structure-based drugs.