title: Antibiotic penetration and bacterial killing in a Pseudomonas aeruginosa biofilm model.
abstract: OBJECTIVE
  Treating biofilm infections successfully is a challenge. We hypothesized that biofilms may be considered as independent compartments with particular pharmacokinetics. We therefore studied the pharmacokinetics and pharmacodynamics of tobramycin in a seaweed alginate-embedded biofilm model.
  
  
  METHODS
  Seaweed alginate beads containing Pseudomonas aeruginosa were cultured in LB medium, sampled at day 1, 3, 5 or 7 and examined for the effect of treatment with tobramycin for 30 min. Treated beads were homogenized and the number of cfu was determined. The antibiotic concentration in the solution of homogenized beads was measured. Finally, beads were examined for live cells by Syto9 staining and for dead cells by propidium iodide staining using a confocal laser scanning microscope.
  
  
  RESULTS
  The antibiotic level in each bead was relatively stable (range 30-42 mg/L; MIC = 1.5 mg/L). There were fewer cfu in the tobramycin-treated beads than the non-treated beads (P < 0.016) and bacterial killing was reduced as the culture period increased from 1 to 7 days. Throughout the study period, increasing size and more superficial positioning of the microcolonies within the beads were demonstrated by confocal laser scanning microscopy. More dead cells (measured by propidium iodide staining) were observed in the treated group of beads, which supports the results obtained by culture.
  
  
  CONCLUSIONS
  The present study, simulating the clinical pharmacokinetics of tobramycin, demonstrates fast absorption of tobramycin in an in vitro biofilm model. In addition, this model system enables parallel investigation of pharmacokinetics and pharmacodynamics, providing a model for testing new treatment strategies.
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark baocao81@gmail.com.
authors: Bao
authors: B
authors: Cao
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Lars
authors: L
authors: Christophersen
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Kim
authors: K
authors: Thomsen
authors: Institute of International Health, Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors: Majken
authors: M
authors: Sønderholm
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.
authors: Peter Østrup
authors: PØ
authors: Jensen
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Niels
authors: N
authors: Høiby
authors: Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark.
authors: Claus
authors: C
authors: Moser
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics* / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D015169:Colony Count, Microbial; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D008962:Models, Theoretical; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000502:physiology; D014031:Tobramycin / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D014031:Tobramycin
keywords: P. aeruginosa; PK/PD; pharmacokinetics/pharmacodynamics