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Antimicrob Agents Chemother. 2015 Jan;59(1):536-43. doi: 10.1128/AAC.04037-14. Epub 2014 Nov 10.

Genomic and transcriptomic analyses of colistin-resistant clinical isolates of Klebsiella pneumoniae reveal multiple pathways of resistance.

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J. Craig Venter Institute, La Jolla, California, USA.
Research Service, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio, USA.
Division of Infectious Diseases, University of North Carolina, Chapel Hill, North Carolina.
Detroit Medical Center, Detroit, Michigan, USA.
Department of Pathology, Case Western Reserve University and University Hospitals Case Medical Center, Cleveland, Ohio, USA.
Research Service, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio, USA Departments of Medicine, Pharmacology, Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, Ohio, USA
J. Craig Venter Institute, La Jolla, California, USA


The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae has resulted in a more frequent reliance on treatment using colistin. However, resistance to colistin (Col(r)) is increasingly reported from clinical settings. The genetic mechanisms that lead to Col(r) in K. pneumoniae are not fully characterized. Using a combination of genome sequencing and transcriptional profiling by RNA sequencing (RNA-Seq) analysis, distinct genetic mechanisms were found among nine Col(r) clinical isolates. Col(r) was related to mutations in three different genes in K. pneumoniae strains, with distinct impacts on gene expression. Upregulation of the pmrH operon encoding 4-amino-4-deoxy-L-arabinose (Ara4N) modification of lipid A was found in all Col(r) strains. Alteration of the mgrB gene was observed in six strains. One strain had a mutation in phoQ. Common among these seven strains was elevated expression of phoPQ and unaltered expression of pmrCAB, which is involved in phosphoethanolamine addition to lipopolysaccharide (LPS). In two strains, separate mutations were found in a previously uncharacterized histidine kinase gene that is part of a two-component regulatory system (TCRS) now designated crrAB. In these strains, expression of pmrCAB, crrAB, and an adjacent glycosyltransferase gene, but not that of phoPQ, was elevated. Complementation with the wild-type allele restored colistin susceptibility in both strains. The crrAB genes are present in most K. pneumoniae genomes, but not in Escherichia coli. Additional upregulated genes in all strains include those involved in cation transport and maintenance of membrane integrity. Because the crrAB genes are present in only some strains, Col(r) mechanisms may be dependent on the genetic background.

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