title: Resistance to the antimicrobial peptide polymyxin requires myristoylation of Escherichia coli and Salmonella typhimurium lipid A.
abstract: Attachment of positively charged, amine-containing residues such as 4-amino-4-deoxy-l-arabinose (l-Ara4N) and phosphoethanolamine (pEtN) to Escherichia coli and Salmonella typhimurium lipid A is required for resistance to the cationic antimicrobial peptide, polymyxin. In an attempt to discover additional lipid A modifications important for polymyxin resistance, we generated polymyxin-sensitive mutants of an E. coli pmrA(C) strain, WD101. A subset of polymyxin-sensitive mutants produced a lipid A that lacked both the 3'-acyloxyacyl-linked myristate (C(14)) and l-Ara4N, even though the necessary enzymatic machinery required to synthesize l-Ara4N-modified lipid A was present. Inactivation of lpxM in both E. coli and S. typhimurium resulted in the loss of l-Ara4N addition, as well as, increased sensitivity to polymyxin. However, decoration of the lipid A phosphate groups with pEtN residues was not effected in lpxM mutants. In summary, we demonstrate that attachment of l-Ara4N to the phosphate groups of lipid A and the subsequent resistance to polymyxin is dependent upon the presence of the secondary linked myristoyl group.
authors.affiliation: Department of Microbiology, J. H. Quillen College of Medicine, Johnson City, Tennessee 37614, USA.
authors.forename: An X
authors.initials: AX
authors.lastname: Tran
authors.forename: Melissa E
authors.initials: ME
authors.lastname: Lester
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Stead
authors.forename: Christian R H
authors.initials: CR
authors.lastname: Raetz
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Maskell
authors.forename: Sara C
authors.initials: SC
authors.lastname: McGrath
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cotter
authors.forename: M Stephen
authors.initials: MS
authors.lastname: Trent
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects*; D006602:Hexosyltransferases / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D019814:Myristic Acid / Q000378:metabolism*; D011113:Polymyxins / Q000494:pharmacology*; D012486:Salmonella typhimurium / Q000187:drug effects*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D008050:Lipid A; D011113:Polymyxins; D019814:Myristic Acid; D000255:Adenosine Triphosphate; D006602:Hexosyltransferases; C442226:L-Ara4N transferase