title: Formation of hydroxyl radicals contributes to the bactericidal activity of ciprofloxacin against Pseudomonas aeruginosa biofilms.
abstract: Antibiotic-tolerant, biofilm-forming Pseudomonas aeruginosa has long been recognized as a major cause of chronic lung infections of cystic fibrosis patients. The mechanisms involved in the activity of antibiotics on biofilm are not completely clear. We have investigated whether the proposed induction of cytotoxic hydroxyl radicals (OH˙) during antibiotic treatment of planktonically grown cells may contribute to action of the commonly used antibiotic ciprofloxacin on P. aeruginosa biofilms. For this purpose, WT PAO1, a catalase deficient ΔkatA and a ciprofloxacin resistant mutant of PAO1 (gyrA), were grown as biofilms in microtiter plates and treated with ciprofloxacin. Formation of OH˙ and total amount of reactive oxygen species (ROS) was measured and viability was estimated. Formation of OH˙ and total ROS in PAO1 biofilms treated with ciprofloxacin was shown but higher levels were measured in ΔkatA biofilms, and no ROS production was seen in the gyrA biofilms. Treatment with ciprofloxacin decreased the viability of PAO1 and ΔkatA biofilms but not of gyrA biofilms. Addition of thiourea, a OH˙ scavenger, decreased the OH˙ levels and killing of PAO1 biofilm. Our study shows that OH˙ is produced by P. aeruginosa biofilms treated with ciprofloxacin, which may contribute to the killing of biofilm subpopulations.
authors.affiliation: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Peter Ø
authors.initials: PØ
authors.lastname: Jensen
authors.forename: Alejandra
authors.initials: A
authors.lastname: Briales
authors.forename: Rikke P
authors.initials: RP
authors.lastname: Brochmann
authors.forename: Hengzhuang
authors.initials: H
authors.lastname: Wang
authors.forename: Kasper N
authors.initials: KN
authors.lastname: Kragh
authors.forename: Mette
authors.initials: M
authors.lastname: Kolpen
authors.forename: Casper
authors.initials: C
authors.lastname: Hempel
authors.forename: Thomas
authors.initials: T
authors.lastname: Bjarnsholt
authors.forename: Niels
authors.initials: N
authors.lastname: Høiby
authors.forename: Oana
authors.initials: O
authors.lastname: Ciofu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development*; D002939:Ciprofloxacin / Q000494:pharmacology*; D003550:Cystic Fibrosis / Q000150:complications; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism*; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D017665:Hydroxyl Radical; D002939:Ciprofloxacin
keywords: Pseudomonas aeruginosa; biofilm; ciprofloxacin; cystic fibrosis; oxidative stress