Novel variant NDM-11 and other NDM-1 variants in multidrug-resistant Escherichia coli from South India

Objectives: Carbapenem resistance mediated by New Delhi metallo-β-lactamase 1 (NDM-1) and its variants has caused a major public-health concern worldwide. Here we report for the first time an Escherichia coli isolate positive for a novel variant (NDM-11). Methods: bla_NDM genes were investigated in E. coli by PCR and sequencing, and bla_NDM variants were further characterised. The susceptibility pattern of novel bla_NDM-11 towards different antimicrobials was compared with bla_NDM-1 by cloning and expression in E. coli TOP10. Results: A total of 33 carbapenem-resistant E. coli isolates were screened by PCR for the presence of bla_NDM, of which 15 (45.5%) were positive. Sequencing of the PCR products revealed 10 isolates with NDM-1 and 5 isolates with NDM variants (one each of NDM-4, NDM-8 and NDM-11 and two NDM-5). Other resistance genes, including bla_TEM-1, bla_CTX-M-15, bla_VIM, plasmid-encoded AmpC bla_CMY-2 and 16S methyltransferases (rmtB and rmtC), were also associated with NDM variants in different combinations. The bla_NDM variants were located on a transferable IncF-type plasmid of >100 kb. Pulsed-field gel electrophoresis (PFGE) showed that all five E. coli isolates were unrelated, and multilocus sequence typing (MLST) revealed that they all belonged to ST131. Expression of the bla_NDM-1 and bla_NDM-11 genes in E. coli TOP10 showed no significant difference in MICs to various β-lactams, including carbapenems. Conclusions: This study underlines the spread of NDM variants with other antimicrobial resistance genes in E. coli in South India. It also describes a novel NDM variant (bla_NDM-11) having an antimicrobial resistance pattern similar to bla_NDM-1.