TY - JOUR T1 - Multifactorial Chromosomal Variants Regulate Polymyxin Resistance in Extensively Drug-Resistant <em>Klebsiella pneumoniae</em> JF - bioRxiv DO - 10.1101/134684 SP - 134684 AU - Miranda E Pitt AU - Alysha G Elliott AU - Minh Duc Cao AU - Devika Ganesamoorthy AU - Ilias Karaiskos AU - Helen Giamarellou AU - Cely S Abboud AU - Mark AT Blaskovich AU - Matthew A Cooper AU - Lachlan Coin Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/05/08/134684.abstract N2 - Objectives Infections facilitated by extensively drug-resistant Klebsiella pneumoniae (XDR-KP) cause high mortality and are disseminating globally. Identifying the genetic basis underpinning resistance allows for rapid diagnosis and treatment.Methods XDR isolates sourced from Greece and Brazil, including nineteen polymyxin-resistant and five polymyxin-susceptible strains, underwent whole genome sequencing.Results Approximately 90% of polymyxin resistance was enabled by alterations upstream or within mgrB. The most common mutation identified was an insertion at nucleotide position 75 in mgrB via an ISKpn26-like element in the ST258 lineage and ISKpn13 in one ST11 isolate. Three strains acquired an IS1 element upstream of mgrB and another strain had an ISKpn25 insertion at 133 bp. Other isolates had truncations (C28STOP, Q30STOP) or a missense mutation (D31E) affecting mgrB. Complementation assays revealed all mgrB perturbations contributed to resistance. Missense mutations in phoQ (T281M, G385C) were also found to facilitate resistance. Several variants in phoPQ co-segregating with the ISKpn26-like insertion were identified as partial suppressor mutations. Three ST258 samples were found to contain subpopulations with different resistance conferring mutations, including the ISKpn26-like insertion colonising with a novel mutation in pmrB (P158R), both confirmed via complementation assays. We also characterized a new multi-drug resistant Klebsiella quasipneumoniae strain ST2401 which was susceptible to polymyxins.Conclusions These findings highlight the broad spectrum of chromosomal modifications which can facilitate and regulate resistance against polymyxins in KP. ER -