Detection of New Delhi Metallo-beta-Lactamase and Extended-Spectrum beta-Lactamase Genes in Escherichia coli Isolated from Mastitic Milk Samples

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 (bla(NDM)). Cloning and sequencing of the PCR amplicon confirmed the identity of the gene (GenBank accession no. ) having 100% homology with bla(NDM-5) (GenBank accession no. ), and this isolate was susceptible to colistin, chloramphenicol and tetracycline only. Moreover, another isolate carried extended-spectrum beta-lactamase (ESBL) gene - bla(CTX-M), and all isolates possessed bla(TEM) 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 (bla(NDM)) 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.