title: Bactericidal effect of colistin on planktonic Pseudomonas aeruginosa is independent of hydroxyl radical formation.
abstract: The bactericidal effect of several major types of antibiotics has recently been demonstrated to be dependent on the formation of toxic amounts of hydroxyl radicals (OH·) resulting from oxidative stress in metabolically active cells. Since killing by the antimicrobial peptide colistin does not require bacterial metabolic activity, we tested whether the bactericidal effect of colistin depends on the formation of OH·. In Pseudomonas aeruginosa cultures, OH-mediated killing by ciprofloxacin was demonstrated by decreased bacterial survival and induction of 3'-(p-hydroxyphenyl) fluorescein (HPF) fluorescence. OH·-mediated killing by ciprofloxacin was further confirmed by rescue of cells and reduction of HPF fluorescence due to prevention of OH· accumulation by scavenging with thiourea, by chelating with dipyridyl, by decreasing metabolism as well as by anoxic growth. In contrast, no formation of OH· was seen in P. aeruginosa during killing by colistin, and prevention of OH· accumulation could not rescue P. aeruginosa from killing by colistin. These results therefore demonstrate that the bactericidal activity of colistin on P. aeruginosa is not dependent on oxidative stress. In conclusion, antimicrobial peptides that do not rely on OH· formation should be considered for treatment of Gram-negative bacteria growing at low oxygen tension such as in endobronchial mucus and paranasal sinuses in cystic fibrosis patients, in abscesses and in infectious biofilm.
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Rikke Prejh
authors: RP
authors: Brochmann
authors: Institute of International Health, Immunology, and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors: Anders
authors: A
authors: Toft
authors: Institute of International Health, Immunology, and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors: Oana
authors: O
authors: Ciofu
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark; Department of Microbiology, University of Seville, Seville, Spain.
authors: Alejandra
authors: A
authors: Briales
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Mette
authors: M
authors: Kolpen
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Casper
authors: C
authors: Hempel
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark; Institute of International Health, Immunology, and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors: Thomas
authors: T
authors: Bjarnsholt
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark; Institute of International Health, Immunology, and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors: Niels
authors: N
authors: Høiby
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark. Electronic address: peter.oestrup.jensen@rh.regionh.dk.
authors: Peter Østrup
authors: PØ
authors: Jensen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism* / Q000633:toxicity*; D050296:Microbial Viability / Q000187:drug effects*; D018384:Oxidative Stress; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D017665:Hydroxyl Radical; D003091:Colistin
keywords: Ciprofloxacin; Colistin; Oxidative stress; Pseudomonas aeruginosa