title: Phototoxic effect of hypericin alone and in combination with acetylcysteine on Staphylococcus aureus biofilms.
abstract: BACKGROUND
  Resistance of bacteria against antibiotics and antimicrobials is arising worldwide and there is an urgent need for strategies that are capable of inactivating biofilm-state pathogens with less potential of developing resistance in pathogens. A promising approach could be photodynamic inactivation (PDI) which uses light in combination with a photosensitizer to induce a phototoxic reaction. In this study, we evaluated the in vitro phototoxic effect of hypericin (HYP) alone and in combination with acetylcysteine (AC) on Staphylococcus aureus biofilms. AC, a mucolytic agent, reduces the production of extracellular polysaccharide matrix while promoting the disruption of mature biofilm.
  
  
  METHODS
  In vitro phototoxic effect of HYP alone (0.5 μg/ml, light dose: 16 J/cm(2)), and in combination with AC (10 mg/ml) on ten clinical S. aureus isolates and S. aureus (ATCC 25923) biofilms was studied. Effect of HYP concentration (0.5 μg/ml) and light dose (8 J/cm(2)) on PDI of all eleven S. aureus strains in planktonic forms was also investigated.
  
  
  RESULTS
  HYP-PDI did not result in a reduction in viable count for each of the strains when grown in biofilms. However, HYP-PDI applied on biofilms treated with AC was able to disrupt pre-formed biofilms (viable count reduction ranging from 5.2 to 6.3 log10-unit in comparison to controls in all tested strains). A 6.5 log killing was obtained for S. aureus (ATCC 25923) planktonic cells treated with 0.5 μg/ml at 8 J/cm(2). For this set of PDI parameters, ten clinical S. aureus isolates showed 5.5-6.7 log killing.
  
  
  CONCLUSIONS
  HYP-PDI in combination with AC had significant ability to eradicate the pre-formed mature biofilms of S. aureus strains.
authors.affiliation: Department of Microbiology, School of Biology, College of Science, University of Tehran, Tehran, Iran. Electronic address: kashefn@khayam.ut.ac.ir.
authors.forename: Nasim
authors.initials: N
authors.lastname: Kashef
authors.affiliation: Department of Microbiology, School of Biology, College of Science, University of Tehran, Tehran, Iran. Electronic address: karami_sh65@ut.ac.ir.
authors.forename: Shima
authors.initials: S
authors.lastname: Karami
authors.affiliation: Iranian Research Center for Medical Lasers, Academic Center for Education, Culture and Research (ACECR), Tehran, Iran. Electronic address: esdjavid@tums.ac.ir.
authors.forename: Gholamreza Esmaeeli
authors.initials: GE
authors.lastname: Djavid
mesh_terms: D000111:Acetylcysteine / Q000008:administration & dosage / Q000494:pharmacology*; D000873:Anthracenes; D018441:Biofilms / Q000187:drug effects*; D004359:Drug Therapy, Combination; D010569:Perylene / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000494:pharmacology*; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D000873:Anthracenes; D017319:Photosensitizing Agents; D011135:Polysaccharides, Bacterial; D010569:Perylene; C004965:hypericin; D000111:Acetylcysteine
keywords: Acetylcysteine; Hypericin; Photodynamic inactivation; Staphylococcus aureus