title: 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.
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Cannatelli
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Giani
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Marco Maria
authors.initials: MM
authors.lastname: D'Andrea
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Di Pilato
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Arena
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors.forename: Viola
authors.initials: V
authors.lastname: Conte
authors.affiliation: Central Public Health Laboratory, Hellenic Centre for Disease Control and Prevention (KEELPNO), Vari, Greece.
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Tryfinopoulou
authors.affiliation: Central Public Health Laboratory, Hellenic Centre for Disease Control and Prevention (KEELPNO), Vari, Greece Department of Microbiology, National School of Public Health, Athens, Greece.
authors.forename: Alkiviadis
authors.initials: A
authors.lastname: Vatopoulos
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Siena, Italy Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy Clinical Microbiology and Virology Unit, Florence Careggi University Hospital, Florence, Italy gianmaria.rossolini@unisi.it.
authors.forename: Gian Maria
authors.initials: GM
authors.lastname: Rossolini
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001618:beta-Lactamases; C063912:carbapenemase; D003091:Colistin