title: Effects of 5-aminolevulinic acid-mediated photodynamic therapy on antibiotic-resistant staphylococcal biofilm: an in vitro study.
abstract: BACKGROUND
  Treatments of infections are not always successful because of multi-antibiotic-resistant organisms. It is therefore particularly urgent to provide more effective anti-infective strategy against these organisms. 5-Aminolevulinic acid (ALA), with the chemical structure C5H9NO3, is the only photodynamic therapy agent that is a biochemical precursor of a photosensitizer (protoporphyrin IX [PpIX]), which is naturally produced by the body. 5-Aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) has been shown to have a strong effect on the treatment of localized cancerous and precancerous lesions, and further study demonstrated its efficacy for gram-positive and gram-negative bacteria. However, its effect on biofilm formed by antibiotic-resistant strains has not been reported.
  
  
  METHODS
  In this study, we evaluated the effectiveness of ALA-PDT on biofilms formed by methicillin-resistant Staphylococcus aureus (ATCC 43300) and methicillin-resistant S epidermidis (MRSE 287). The strains were cultured with 40 mM of ALA in 24-well microtiter plates containing coverslips at 37°C for 24 h in the dark. PpIX fluorescence in biofilms formed by the two strains was observed by confocal laser scanning microscopy (CLSM). ALA-treated biofilms were irradiated at different doses (0, 100, 200, and 300 J/cm(2)) using a semiconductor laser. Biofilm exposed only to Tryptone Soy Broth or irradiation (300 J/cm(2)) was investigated. Viability determination, CLSM, and scanning electron microscopy were used to investigate the photodynamic inactivation of ALA-PDT.
  
  
  RESULTS
  ALA was absorbed and converted to PpIX by both methicillin-resistant S aureus and methicillin-resistant S epidermidis. No cell inactivation was detectable in biofilms of either strain incubated with ALA without exposure to light, incubated with Tryptone Soy Broth only, or irradiated with red light only. However, a significant number of cells within biofilms were inactivated during irradiation with different doses of red light in the presence of 40 mM of ALA in a dose-dependent manner. The drastic reduction in cell survival within biofilms and the disruption of biofilms were confirmed by CLSM and scanning electron microscopy.
  
  
  CONCLUSIONS
  ALA-PDT has the potential to eliminate the biofilm of Staphylococcus, especially antibiotic-resistant strains, effectively. It will be suitable for the treatment of superficial local infections such as surface wounds, burns, oral and dental infections, dermatologic infections such as acne and rosacea, and soft tissue and bone infections with bone exposure.
authors.affiliation: The Central Hospital of Xuzhou, Affiliated Xuzhou Hospital, Medical College of Southeast University, Xuzhou, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Hao
authors.initials: H
authors.lastname: Guo
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Tian
authors.forename: Gang
authors.initials: G
authors.lastname: Zheng
authors.forename: Yangchao
authors.initials: Y
authors.lastname: Hu
authors.forename: Yu
authors.initials: Y
authors.lastname: Fu
authors.forename: Honglue
authors.initials: H
authors.lastname: Tan
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology*; D000818:Animals; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development / Q000528:radiation effects*; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D066298:In Vitro Techniques; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D010778:Photochemotherapy / Q000379:methods*; D011524:Protoporphyrins / Q000378:metabolism; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D016896:Treatment Outcome
chemical_list: D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX
keywords: Aminolevulinic acid; Biofilm; MRSA; MRSE; Photodynamic therapy