Colistin resistance due to insertional inactivation of the mgrB in Klebsiella pneumoniae of clinical origin: First report from India.

OBJECTIVE

Mutations in mgrB, phoP/phoQ, pmrA, pmrB, pmrC, and crrABC regulatory systems have been found responsible for colistin resistance. The aim of our study was to investigate the role of alteration in mgrB gene and plasmid mediate mcr-1 and mcr-2 genes as a source of colistin resistance in 17 non duplicate Klebsiella pneumoniae clinical isolates.

METHODS

All isolates classified as resistant to colistin by VITEK 2 system (BioMerieux, Marcy I' Etoile, France) were included. Susceptibility to colistin was also determined by broth microdilution using breakpoints recommended by EUCAST (>2mg/L resistant; and ≤2mg/L susceptible). PCR amplification of mgrB gene was performed and sequenced using specific primers. Presence of mcr-1 and mcr-2 was also investigated using PCR.

RESULTS

PCR amplification of the mgrB gene of the 17 K.pneumoniae isolates revealed a larger (~1000bp) amplicon in three isolates when compared with the wild type mgrB ampiclon (250 bp). Sequencing of these amplicons showed that mgrB was disrupted by the insertion of ISKpn14, a IS element belonging to the IS1 family. Sequencing, of the 250 bp mgrB gene in the remaining 14 isolates revealed frame shift mutation after the second codon leading to a premature stop codon in only one isolate.

CONCLUSIONS

The study showed that colistin resistance in 20% of the K. pneumoniae isolates was due to loss of function of mgrB. We describe for the first-time from India, insertional inactivation of mgrB by ISKpn14 inserted at different sites, responsible for colistin resistance.