title: Modulation of mgrB gene expression as a source of colistin resistance in Klebsiella oxytoca.
abstract: Gene modifications in the PmrAB and PhoPQ two-component regulatory systems, as well as inactivation of the mgrB gene, are known to be causes of colistin resistance in Klebsiella pneumoniae. The objective of this study was to characterise the mechanism involved in colistin resistance in a Klebsiella oxytoca isolate. A K. oxytoca clinical isolate showing resistance to colistin was recovered in Cali, Colombia. The pmrA, pmrB, phoP, phoQ and mgrB genes were amplified and sequenced. Wild-type mgrB genes from K. pneumoniae and K. oxytoca were cloned, and corresponding recombinant plasmids were used for complementation assays. By analysing the mgrB gene of the K. oxytoca isolate and its flanking sequences, an insertion sequence (IS) of 1196bp was identified in its promoter region. The insertion was located between nucleotides -39 and -38 when referring to the start codon of the mgrB gene, thus negatively interfering with expression of the mgrB gene by modifying its promoter structure. This IS was very similar to ISKpn26 (99% nucleotide identity) belonging to the IS5 family. Complementation assays with mgrB genes from wild-type K. pneumoniae or K. oxytoca restored full susceptibility to colistin. In conclusion, here we identified the mechanism involved in colistin resistance in a K. oxytoca isolate. Modulation of mgrB gene expression was the key factor for this acquired resistance to colistin.
authors.affiliation: Medical and Molecular Microbiology «Emerging Antibiotic Resistance» Unit, Department of Medicine, Faculty of Science, University of Fribourg, Rue Albert-Gockel 3, CH-1700 Fribourg, Switzerland.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Jayol
authors.affiliation: Medical and Molecular Microbiology «Emerging Antibiotic Resistance» Unit, Department of Medicine, Faculty of Science, University of Fribourg, Rue Albert-Gockel 3, CH-1700 Fribourg, Switzerland. Electronic address: laurent.poirel@unifr.ch.
authors.forename: Laurent
authors.initials: L
authors.lastname: Poirel
authors.affiliation: International Center for Medical Research and Training, CIDEIM, Cali, Colombia.
authors.forename: Maria-Virginia
authors.initials: MV
authors.lastname: Villegas
authors.affiliation: Medical and Molecular Microbiology «Emerging Antibiotic Resistance» Unit, Department of Medicine, Faculty of Science, University of Fribourg, Rue Albert-Gockel 3, CH-1700 Fribourg, Switzerland; Hôpital Fribourgeois - Hôpital Cantonal de Fribourg, Riaz, Switzerland.
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003001:Cloning, Molecular; D003091:Colistin / Q000494:pharmacology*; D003105:Colombia; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D015870:Gene Expression; D005816:Genetic Complementation Test; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D041121:Klebsiella oxytoca / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D008565:Membrane Proteins; D003091:Colistin
keywords: PhoPQ regulatory system; Polymyxin; Resistance