title: Sublethal ciprofloxacin treatment leads to rapid development of high-level ciprofloxacin resistance during long-term experimental evolution of Pseudomonas aeruginosa.
abstract: The dynamics of occurrence and the genetic basis of ciprofloxacin resistance were studied in a long-term evolution experiment (940 generations) in wild-type, reference strain (PAO1) and hypermutable (PAOΔmutS and PAOMY-Mgm) P. aeruginosa populations continuously exposed to sub-MICs (1/4) of ciprofloxacin. A rapid occurrence of ciprofloxacin-resistant mutants (MIC of ≥12 μg/ml, representing 100 times the MIC of the original population) were observed in all ciprofloxacin-exposed lineages of PAOΔmutS and PAOMY-Mgm populations after 100 and 170 generations, respectively, and in one of the PAO1 lineages after 240 generations. The genetic basis of resistance was mutations in gyrA (C248T and G259T) and gyrB (C1397A). Cross-resistance to beta-lactam antibiotics was observed in the bacterial populations that evolved during exposure to sublethal concentrations of ciprofloxacin. Our study shows that mutants with high-level ciprofloxacin resistance are selected in P. aeruginosa bacterial populations exposed to sub-MICs of ciprofloxacin. This can have implications for the long-term persistence of resistant bacteria and spread of antibiotic resistance by exposure of commensal bacterial flora to low antibiotic concentrations.
authors.affiliation: Department of International Health, Immunology and Microbiology, Unit of Bacteriology, Costerton Biofilm Centre, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Karin Meinike
authors.initials: KM
authors.lastname: Jørgensen
authors.forename: Tina
authors.initials: T
authors.lastname: Wassermann
authors.forename: Peter Østrup
authors.initials: PØ
authors.lastname: Jensen
authors.forename: Wang
authors.initials: W
authors.lastname: Hengzuang
authors.forename: Søren
authors.initials: S
authors.lastname: Molin
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*; D002939:Ciprofloxacin / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D017422:Sequence Analysis, DNA; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D002939:Ciprofloxacin; D027081:DNA Gyrase