In this study, eight Escherichia coli isolates were obtained from milk samples of dairy cattle suffering from clinical/subclinical mastitis. Isolates were characterized for antimicrobial resistance traits and virulence genes. Results revealed that one isolate was harbouring New Delhi metallo-beta-lactamase gene (blaNDM ). Cloning and sequencing of the PCR amplicon confirmed the identity of the gene (GenBank accession no. KC769583) having 100% homology with blaNDM-5 (GenBank accession no. JN104597.1), and this isolate was susceptible to colistin, chloramphenicol and tetracycline only. Moreover, another isolate carried extended-spectrum beta-lactamase (ESBL) gene - blaCTX-M , and all isolates possessed blaTEM gene. Of the eight isolates, only one isolate was positive for shiga toxin gene (stx2), and none were harbouring stx1 gene. Occurrence of New Delhi metallo-beta-lactamase (blaNDM ) in one E. coli isolate and ESBL genes in other isolates poses a potential threat to human health following possible entry and spread through food chain.

Emergence of antimicrobial resistance mediated through New Delhi metallo-β-lactamases (NDMs) is a serious therapeutic challenge. Till date, 16 different NDMs have been described. In this study, we report the molecular and structural characteristics of NDM-5 isolated from an Escherichia coli isolate (KOEC3) of bovine origin. Using PCR amplification, cloning and sequencing of full blaNDM gene, we identified the NDM type as NDM-5. Cloning of full gene in E. coli DH5α and subsequent assessment of antibiotic susceptibility of the transformed cells indicated possible role of native promoter in expression blaNDM-5. Translated amino acid sequence had two substitutions (Val88Leu and Met154Leu) compared to NDM-1. Theoretically deduced isoelectric pH of NDM-5 was 5.88 and instability index was 36.99, indicating a stable protein. From the amino acids sequence, a 3D model of the protein was computed. Analysis of the protein structure elucidated zinc coordination and also revealed a large binding cleft and flexible nature of the protein, which might be the reason for broad substrate range. Docking experiments revealed plausible binding poses for five carbapenem drugs in the vicinity of metal ions. In conclusion, results provided possible explanation for wide range of antibiotics catalyzed by NDM-5 and likely interaction modes with five carbapenem drugs.