title: In vivo emergence of colistin resistance in Klebsiella pneumoniae producing KPC-type carbapenemases mediated by insertional inactivation of the PhoQ/PhoP mgrB regulator.
abstract: Colistin is one of the few agents that retain activity against extensively drug-resistant strains of Klebsiella pneumoniae producing KPC-type carbapenemases (KPC-KP). However, resistance to colistin is increasingly reported among KPC-KP. Comparative genomic analysis of a pair of sequential KPC-KP isolates from the same patient including a colistin-susceptible isolate (KKBO-1) and a colistin-resistant isolate (KKBO-4) selected after colistin exposure revealed that insertional inactivation of the mgrB gene, encoding a negative regulator of the PhoQ/PhoP signaling system, is a genetic mechanism for acquired colistin resistance. The role of mgrB inactivation in acquired colistin resistance was confirmed by complementation experiments with wild-type mgrB, which restored colistin susceptibility in KKBO-4, and by construction of an mgrB deletion mutant from KKBO-1, which exhibited a colistin-resistant phenotype. Insertional mgrB inactivation was also detected in 60% of colistin-resistant mutants selected from KKBO-1 in vitro, following plating on colistin-containing medium, confirming the role (although not unique) of this mechanism in the emergence of acquired colistin resistance. In colistin-resistant mutants carrying insertional inactivation or deletion of the mgrB gene, upregulated transcription of phoP, phoQ, and pmrK (which is part of the pmrHFIJKLM operon) was detected. These findings confirmed the MgrB regulatory role in K. pneumoniae and were in agreement with the known association between upregulation of the PhoQ/PhoP system and activation of the pmrHFIJKLM operon, which eventually leads to resistance to polymyxins by modification of the lipopolysaccharide target.
authors: Department of Medical Biotechnologies, University of Siena, Siena, Italy.
authors: Antonio
authors: A
authors: Cannatelli
authors: Marco Maria
authors: MM
authors: D'Andrea
authors: Tommaso
authors: T
authors: Giani
authors: Vincenzo
authors: V
authors: Di Pilato
authors: Fabio
authors: F
authors: Arena
authors: Simone
authors: S
authors: Ambretti
authors: Paolo
authors: P
authors: Gaibani
authors: Gian Maria
authors: GM
authors: Rossolini
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D003091:Colistin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005809:Genes, Regulator; D006801:Humans; D007710:Klebsiella Infections / Q000188:drug therapy / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009876:Operon; D015398:Signal Transduction; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D008565:Membrane Proteins; C079792:PhoQ protein, Bacteria; C061064:PhoP protein, Bacteria; D001618:beta-Lactamases; C063912:carbapenemase; D003091:Colistin
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