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 genes were investigated in E. coli by PCR and sequencing, and bla variants were further characterised. The susceptibility pattern of novel bla towards different antimicrobials was compared with bla 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, 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, bla, bla, plasmid-encoded AmpC bla and 16S methyltransferases (rmtB and rmtC), were also associated with NDM variants in different combinations. The bla variants were located on a transferable IncF-type plasmid of >100kb. 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 and bla 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) having an antimicrobial resistance pattern similar to bla.