Molecular and computational approaches to understand resistance of New Delhi metallo β-lactamase variants (NDM-1, NDM-4, NDM-5, NDM-6, NDM-7)-producing strains against carbapenems.

The discovery of NDM-1 and its variants has caused the emergence of antibiotic resistance in the community and hospital setting, causing major concern for health care across the globe. New Delhi Metallo-β-lactamase is known to hydrolyse almost all β-lactam antibiotics. Studies have shown the hydrolytic activates of NDM-1 and some of its variants, however a comparative study of these NDM variants has not been explored in detail. Hence, we proposed to check their catalytic activity by performing a comparative study between NDM-1 and its variants. The study was initiated to clone NDM variants (NDM-1, NDM-4, NDM-5, NDM-6 and NDM-7) followed by overexpression of the recombinant proteins to check their hydrolytic properties against β-lactam antibiotics. The minimum inhibitory concentration of carbapenems antibiotics for blaNDM-5 clone was found four fold increased, whereas no change was observed in the clones having other variants. The hydrolytic activity of carbapenem with NDM-5 variant was found to be augmented as per the kinetics parameter where Km was decreased and kcat, kcat/Km values increased as compared to the NDM-1. Molecular docking studies were employed to identify the variations in the binding ability among all NDM variants with imipenem or meropenem. Simulation studies at 100 ns showed a good stability of NDM-5 with imipenem and meropenem as compared to NDM-1. CD spectroscopy data revealed significant changes in the secondary structure of NDM variants. We conclude that NDM-5 showed higher hydrolytic activity as compared to other variants. This study provides a comparative analysis of the severity of NDM producing strains.