MgrB inactivation is a common mechanism of colistin resistance in KPC-producing Klebsiella pneumoniae of clinical origin

Abstract

Klebsiella pneumoniae strains producing KPC-type carbapenemases (KPC-KP) are challenging multidrug-resistant pathogens due to their extensively drug-resistant phenotypes and potential for epidemic dissemination in health care settings. Colistin is a key component of the combination antimicrobial regimens used for treatment of severe KPC-KP infections. We previously reported that insertional inactivation of the mgrB gene, encoding a negative-feedback regulator of the PhoQ-PhoP signaling system, can be responsible for colistin resistance in KPC-KP, due to the resulting upregulation of the Pmr lipopolysaccharide modification system. In this work we investigated the status of the mgrB gene in a collection of 66 colistin-resistant nonreplicate clinical strains of KPC-KP isolated from different hospitals in Italy and Greece. Overall, 35 strains (53%) exhibited alterations of the mgrB gene, including insertions of different types of mobile elements (IS5-like, IS1F-like, or ISKpn14), nonsilent point mutations, and small intragenic deletions. Four additional strains had a larger deletion of the mgrB locus, while the remaining 27 strains (41%) did not show mgrB alterations. Transcriptional upregulation of the phoQ and pmrK genes (part of the phoPQ and pmrHFIJKLM operon, respectively) was observed in all strains with mgrB alterations. Complementation experiments with a wild-type mgrB gene restored colistin susceptibility and basal expression levels of phoQ and pmrK genes in strains carrying different types of mgrB alterations. The present results suggest that mgrB alteration can be a common mechanism of colistin resistance among KPC-KP in the clinical setting.

FIG 1

Geographical distribution of the Greek and Italian centers from which COL-R strains were originated. Centers where strains carrying mgrB lesions were detected are circled. The number of each center corresponds to the location as follows: IT-1, Lecco; IT-2, Turin; IT-3, Genoa; IT-4, Pietra Ligure; IT-5, Verona; IT-6, Milan; IT-7, Pavia; IT-8-9, Modena; IT-10, San Remo; IT-11, Florence; IT-12, Ancona; IT-13, Rome; IT-14, Foggia; IT-15, Naples; IT-16, Lecce; IT-17, Cosenza; IT-18, Palermo; IT-19, Catania; GR-1, Salonika; GR-2, Agrinio; GR-3-4, Athens.

FIG 2

Map of the K. pneumoniae chromosomal region carrying the mgrB gene. The map is drawn based on sequence information from the K. pneumoniae HS11286 chromosome (GenBank accession no. CP000649) (19). Open reading frames are indicated by arrows (arrow direction indicates orientation). The locations of primers used for PCR mapping of the mgrB locus are indicated by thin black arrows (1F, EE_mgrB_F; 1R, EE_mgrB_R; 2F, mgrB_Ext_F; 2R, mgrB_Ext_R; 3F, Int_mgrB_F; 3R, Int_mgrB_R). The expected sizes of the PCR products are also shown.