title: Activity of the type I signal peptidase inhibitor MD3 against multidrug-resistant Gram-negative bacteria alone and in combination with colistin.
abstract: OBJECTIVE
  Effective treatment of Gram-negative bacterial infections is increasingly challenging due to the spread of multidrug-resistant strains and a lack of new antimicrobials in development. Bacterial type I signal peptidases (SPases) represent a highly conserved and essential target for inhibition by novel compounds. SPases are required for the effective processing of membrane translocated proteins involved in core functions related to metabolism, virulence and resistance. In this study we assessed the biochemical and functional activity of a novel synthetic inhibitor (MD3) of SPases against a wide range of Gram-negative pathogens.
  
  
  METHODS
  The activity and specificity of MD3 for recombinant Pseudomonas aeruginosa SPase (LepB) and a genetically engineered LepB-regulatable strain were investigated. Antimicrobial activity of the compound alone and in combination with outer membrane-permeabilizing agents (sodium hexametaphosphate, colistin) was also determined against a collection of P. aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia isolates.
  
  
  RESULTS
  MD3 was found to inactivate the P. aeruginosa LepB protein (IC50 10 μM), resulting in antimicrobial effects potentiated in the presence of colistin. MD3 also demonstrated potent activity against wild-type and multidrug-resistant strains of A. baumannii and S. maltophilia with MICs ranging from 0.5 to 14 mg/L in the presence of subinhibitory concentrations of colistin.
  
  
  CONCLUSIONS
  MD3 is a novel inhibitor of bacterial SPase in a range of non-fermentative Gram-negative bacteria. The antimicrobial activity is potentiated in combination with colistin and suggests that SPase inhibition warrants further exploration as a basis for future mono or combination therapies.
authors.affiliation: Centre for Immunology and Infectious Disease, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, 4 Newark Street, London E1 2AT, UK.
authors.forename: Yoann
authors.initials: Y
authors.lastname: Personne
authors.affiliation: Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, 4 Newark Street, London E1 2AD, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Curtis
authors.affiliation: Centre for Immunology and Infectious Disease, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, 4 Newark Street, London E1 2AT, UK.
authors.forename: David W
authors.initials: DW
authors.lastname: Wareham
authors.affiliation: Centre for Immunology and Infectious Disease, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, 4 Newark Street, London E1 2AT, UK richard.d.waite@gmail.com.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Waite
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000201:enzymology*; D020128:Inhibitory Concentration 50; D008565:Membrane Proteins / Q000037:antagonists & inhibitors*; D008826:Microbial Sensitivity Tests; D012697:Serine Endopeptidases
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D012697:Serine Endopeptidases; C026515:type I signal peptidase; D003091:Colistin
keywords: MDR; antibiotic synergy; novel therapies