title: The phenotypic evolution of Pseudomonas aeruginosa populations changes in the presence of subinhibitory concentrations of ciprofloxacin.
abstract: Ciprofloxacin is a widely used antibiotic, in the class of quinolones, for treatment of Pseudomonas aeruginosa infections. The immediate response of P. aeruginosa to subinhibitory concentrations of ciprofloxacin has been investigated previously. However, the long-term phenotypic adaptation, which identifies the fitted phenotypes that have been selected during evolution with subinhibitory concentrations of ciprofloxacin, has not been studied. We chose an experimental evolution approach to investigate how exposure to subinhibitory concentrations of ciprofloxacin changes the evolution of P. aeruginosa populations compared to unexposed populations. Three replicate populations of P. aeruginosa PAO1 and its hypermutable mutant ΔmutS were cultured aerobically for approximately 940 generations by daily passages in LB medium with and without subinhibitory concentration of ciprofloxacin and aliquots of the bacterial populations were regularly sampled and kept at  - 80 °C for further investigations. We investigate here phenotypic changes between the ancestor (50 colonies) and evolved populations (120 colonies/strain). Decreased protease activity and swimming motility, higher levels of quorum-sensing signal molecules and occurrence of mutator subpopulations were observed in the ciprofloxacin-exposed populations compared to the ancestor and control populations. Transcriptomic analysis showed downregulation of the type III secretion system in evolved populations compared to the ancestor population and upregulation of denitrification genes in ciprofloxacin-evolved populations. In conclusion, the presence of antibiotics at subinhibitory concentration in the environment affects bacterial evolution and further studies are needed to obtain insight into the dynamics of the phenotypes and the mechanisms involved.
authors.affiliation: Department of Clinical Microbiology, University Hospital Rigshospitalet, Copenhagen, Denmark.
authors.forename: Tina
authors.initials: T
authors.lastname: Wassermann
authors.affiliation: Department of Immunology and Microbiology, Costerton Biofilm Center, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Karin
authors.initials: K
authors.lastname: Meinike Jørgensen
authors.affiliation: Department of Immunology and Microbiology, Costerton Biofilm Center, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Karolina
authors.initials: K
authors.lastname: Ivanyshyn
authors.affiliation: Department of Clinical Microbiology, University Hospital Rigshospitalet, Copenhagen, Denmark.|Department of Immunology and Microbiology, Costerton Biofilm Center, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bjarnsholt
authors.affiliation: Department of System Biology, Technical University of Denmark, Lyngby, Denmark.
authors.forename: S M Hossein
authors.initials: SMH
authors.lastname: Khademi
authors.affiliation: Department of System Biology, Technical University of Denmark, Lyngby, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Jelsbak
authors.affiliation: Department of Clinical Microbiology, University Hospital Rigshospitalet, Copenhagen, Denmark.|Department of Immunology and Microbiology, Costerton Biofilm Center, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Niels
authors.initials: N
authors.lastname: Høiby
authors.affiliation: Department of Immunology and Microbiology, Costerton Biofilm Center, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Oana
authors.initials: O
authors.lastname: Ciofu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D058440:Denitrification / Q000235:genetics; D008826:Microbial Sensitivity Tests; D051719:MutS DNA Mismatch-Binding Protein / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000472:pathogenicity*; D053038:Quorum Sensing / Q000235:genetics; D000069296:Type III Secretion Systems / Q000235:genetics; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D000069296:Type III Secretion Systems; D037521:Virulence Factors; D002939:Ciprofloxacin; D051719:MutS DNA Mismatch-Binding Protein