title: Starvation- and antibiotics-induced formation of persister cells in Pseudomonas aeruginosa.
abstract: BACKGROUND
  Planktonic stationary and exponential cultures of Pseudomonas aeruginosa are highly resistant to killing by bactericidal antimicrobials because of the presence of persisters, cells that are multidrug tolerant and play a key role in the recalcitrance of biofilm infections.
  
  
  OBJECTIVE
  The aim of this study was to investigate the formation of persister cells in P. aeruginosa stationary vs. exponential cultures using different class antimicrobials.
  
  
  METHODS
  The susceptibilities of P. aeruginosa PAO1 wild-type and mutant strains to antimicrobials were determined by standard microtiter broth dilution method. In order to determine persister formation, dose- and time-dependent killing experiments were performed with antibiotics.
  
  
  RESULTS
  Ceftazidime (Cephalosporin) showed little efficacy against either culture. Stationary-phase cells were more tolerant to imipenem (Carbapenem) than exponential cells, leaving a small fraction of persisters at high imipenem concentration in both populations. Polymyxin B (Polymyxin) appeared to be ineffective at low concentrations against both cell populations. Very high polymyxin B concentration completely eradicated exponential cells and regrowth was seen in a stationary population. Stationary cells were more tolerant to tobramycin (Aminoglycoside) than exponential cells but a higher concentration of tobramycin completely eliminated survivors. Ciprofloxacin (Fluoroquinolone) at a low concentration resulted in killing of both cultures of P. aeruginosa, producing persisters that were invulnerable to killing.
  
  
  CONCLUSIONS
  Stationary cells appear to be somewhat more tolerant than exponential cells in all of these assays. We also showed that nutrient deprivation (serine starvation) regulated by stringent and general stress response, contribute to the increased tolerance of P. aeruginosa exponential and stationary planktonic cells via production of persisters.
authors.affiliation: Department of Microbiology, Faculty of Medicine and Dentistry, Palacky University Olomouc, Czech Republic.
authors.forename: Patrik
authors.initials: P
authors.lastname: Mlynarcik
authors.affiliation: Department of Microbiology, Faculty of Medicine and Dentistry, Palacky University Olomouc, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Kolar
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D012694:Serine / Q000172:deficiency
chemical_list: D000900:Anti-Bacterial Agents; D012694:Serine
keywords: P. aeruginosa; antimicrobials; mutant; persisters; planktonic; serine hydroxamate; tolerance