title: Phototoxicity of phenothiazinium dyes against methicillin-resistant Staphylococcus aureus and multi-drug resistant Escherichia coli.
abstract: BACKGROUND
  Photodynamic inactivation (PDI) has been investigated to cope with the increasing incidence of multidrug-resistant (MDR) pathogens. Here we studied the PDI mediated by methylene blue (MB) and toluidine blue O (TBO) in clinical methicillin-resistant Staphylococcus aureus and MDR Escherichia coli, together with their corresponding American Type Culture Collection (ATCC) strains.
  
  
  METHODS
  Effect of photosensitizer concentration (12.5, 25, 50 μg/ml) and laser irradiation time (10, 20 and 30 min) on lethal photosensitization was investigated.
  
  
  RESULTS
  TBO was more effective. TBO at 50 μg/ml, 46.8 J cm⁻², exhibited 0.7 log killing for MDR E. coli and 1.7 log killing for E. coli (ATCC 25922); 3.1 log killing for MRSA, and 4.2 log killing for S. aureus (ATCC 25923). MB at 50 μg/ml, 163.8 J cm⁻², only exhibited 2.2 log killing in MRSA and 3.1 log killing in S. aureus (ATCC 25923). MB (50 μg/ml, 163.8 J cm⁻²) induced 0.2 log killing for MDR E. coli and 0.3 log killing for E. coli (ATCC 25922). After TBO-PDI, MDR isolates were more susceptible to some antibiotics than control groups.
  
  
  CONCLUSIONS
  Our studied clinical isolates were more resistant to PDI-mediated killing than their ATCC reference strains. Thus, TBO/MB-mediated PDI in other MDR isolates deserves further investigation.
authors.affiliation: Department of Microbiology, School of Biology, College of Science, University of Tehran, Tehran, Iran. kashefn@khayam.ut.ac.ir
authors.forename: Nasim
authors.initials: N
authors.lastname: Kashef
authors.forename: Gita
authors.initials: G
authors.lastname: Ravaei Sharif Abadi
authors.forename: Gholamreza Esmaeeli
authors.initials: GE
authors.lastname: Djavid
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology; D001431:Bacteriological Techniques; D004396:Coloring Agents / Q000008:administration & dosage / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D004926:Escherichia coli / Q000187:drug effects*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008751:Methylene Blue / Q000008:administration & dosage / Q000494:pharmacology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000494:pharmacology*; D014048:Tolonium Chloride / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004396:Coloring Agents; D017319:Photosensitizing Agents; D014048:Tolonium Chloride; D008751:Methylene Blue