title: Molecular basis for the increased polymyxin susceptibility of Klebsiella pneumoniae strains with under-acylated lipid A.
abstract: The impact of under-acylation of lipid A on the interaction between Klebsiella pneumoniae LPS and polymyxins B and E was examined with fluorometric and calorimetric methods, and by (1)H NMR, using a paired wild type (WT) and the ΔlpxM mutant strains B5055 and B5055ΔlpxM, which predominantly express LPS with hexa- and penta-acylated lipid A structures respectively. LPS from B5055ΔlpxM displayed a fourfold increased binding affinity for polymyxins B and E compared with the B5055 WT LPS. EC50 values were consistent with polymyxin minimum inhibitory concentration (MIC) values for each strain. Accordingly, polymyxin exposure considerably enhanced the permeability of the B5055ΔlpxM OM. Analysis of the melting profiles of isolated LPS aggregates suggested that bactericidal polymyxin activity may relate to the acyl chains' phase of the outer membrane (OM). The enhanced polymyxin susceptibility of B5055ΔlpxM may be attributable to the favorable insertion of polymyxins into the more fluid OM compared with B5055. Molecular models of the polymyxin B-lipid A complex illuminate the key role of the lipid A acyl chains for complexation of polymyxin. The data provide important insight into the molecular basis for the increased polymyxin susceptibility of K. pneumoniae strains with under-acylated lipid A. Under-acylation appears to facilitate the integration of the N-terminal fatty-acyl chain of polymyxin into the OM resulting in an increased susceptibility to its antimicrobial activity/activities.
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.
authors.forename: Tony
authors.initials: T
authors.lastname: Velkov
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Soon
authors.forename: Pei L
authors.initials: PL
authors.lastname: Chong
authors.forename: Johnny X
authors.initials: JX
authors.lastname: Huang
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Cooper
authors.forename: Mohammad A K
authors.initials: MA
authors.lastname: Azad
authors.forename: Mark A
authors.initials: MA
authors.lastname: Baker
authors.forename: Philip E
authors.initials: PE
authors.lastname: Thompson
authors.forename: Kade
authors.initials: K
authors.lastname: Roberts
authors.forename: Roger L
authors.initials: RL
authors.lastname: Nation
authors.forename: Abigail
authors.initials: A
authors.lastname: Clements
authors.forename: Richard A
authors.initials: RA
authors.lastname: Strugnell
authors.forename: Jian
authors.initials: J
authors.lastname: Li
mesh_terms: D000215:Acylation / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000235:genetics; D003091:Colistin / Q000737:chemistry / Q000494:pharmacology*; D003198:Computer Simulation; D005227:Fatty Acids / Q000737:chemistry; D006801:Humans; D007710:Klebsiella Infections / Q000188:drug therapy* / Q000276:immunology; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000235:genetics / Q000276:immunology; D008050:Lipid A / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011112:Polymyxin B / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D005227:Fatty Acids; D008050:Lipid A; D011112:Polymyxin B; D003091:Colistin