title: In vitroActivity of Linezolid in Combination with Photodynamic Inactivation AgainstStaphylococcus aureusBiofilms.
abstract: BACKGROUND
  Biofilm infections are a major challenge in medical practice. Bacteria that live in a biofilm phenotype are more resistant to both antimicrobial therapy and host immune responses compared to their planktonic counterparts. So, there is need for new therapeutic strategies to combat these infections. A promising approach [known as Photodynamic Inactivation (PDI)] to kill bacteria growing as biofilms uses light in combination with a photosensitizer to induce a phototoxic reaction which produces reactive oxygen species that can destroy lipids and proteins causing cell death. PDI does not always guarantee full success, so, combination of PDI with antibiotics may give increased efficiency. This study aimed to determine if PDI was effective in the eradication ofStaphylococcus aureus(S. aureus) biofilms in combination with linezolid.
  
  
  METHODS
  The susceptibility of biofilm cultures of threeS. aureusstrains to Methylene Blue (MB) and Toluidine Blue O (TBO)-mediated PDI was determined alone and in combination with linezolid.
  
  
  RESULTS
  Bactericidal activity (≥3 log10reduction in viable cell count) was not achieved with MB/TBO-PDI or antibiotic treatment alone. When antibiotic treatment was combined with TBO-PDI, a greater reduction in viable count than antibiotic alone was observed for two strains.
  
  
  CONCLUSIONS
  This study showed that although TBO-PDI did not have good bactericidal activity againstS. aureusbiofilms; it increased the antimicrobial activity of linezolid against these bacteria.
authors.affiliation: Department of Microbiology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Nasim
authors.initials: N
authors.lastname: Kashef
authors.affiliation: Department of Microbiology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Mahboobeh
authors.initials: M
authors.lastname: Akbarizare
authors.affiliation: Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Razzaghi
keywords: Antibiotic therapy; Biofilm; Photodynamic inactivation; Staphylococcus aureus