Photodynamic Disinfection (PDD) is the Antimicrobial application of PDT (aPDT)

The key features of aPDT can be summarized as follows [1]:

  • Broad spectrum of action, since one photosensitizer can act on bacteria, fungi, yeasts and parasitic protozoa
  • Efficacy independent of the resistance pattern of the given microbe
  • Extensive reduction of pathogen counts in minutes, without damaging host cells
  • No selection of resistant strains after multiple treatments
  • Readily available, non-toxic photosensitizers
  • Relatively low-cost light sources for activation of the photosensitizing agent
  • No cytotoxic effects on key sensitive host cells such as human keratinocytes or fibroblasts

The treatment of topical infections has traditionally relied upon antibiotics in either topical or systemic dosage forms. However, the inexorable increase in antibiotic resistance (including to vancomycin and other glycopeptides) has led to the spectre of potentially untreatable infections, and this in turn has led to the development of alternative antimicrobial approaches based on light-activated chemotherapy 2, 3. Photodynamic Disinfection (called antimicrobial PDT by the scientific community) is an extension to traditional photodynamic therapy (PDT) which was originally focused on oncotherapy and intra-ocular indications, utilizing systemically-administered photosensitizers.

The antimicrobial PDT (aPDT) approach utilizes topically-applied sensitizers, avoiding systemic phototoxicity, and targets microbial biofilms with high specificity and efficacy.  Biofilms are formed when colonizing microbes encapsulate themselves against host surfaces in an exopolymeric matrix composed of secreted polysaccharides, proteins, and nucleic acids. Close proximity of one cell to another permits information exchange through quorum sensing and plasmid DNA transfer, with resulting survival advantages conferred across the entire colony. Biofilms are much more difficult to eradicate by conventional means (i.e. antibiotics or debridement) than planktonic microbial colonies, because of the strong tissue adherence and physical exclusion of antimicrobial substances in the biofilm form.

Sensitizers used for aPDT photodisinfection are generally low-molecular-weight, cationic, hydrophilic stains capable of rapidly penetrating dense microbial biofilms while only minimally affecting human tissue.  Once activated by light of the appropriate wavelength, these agents efficiently produce singlet oxygen and other oxidative radicals with high quantum yield, resulting in potent, broad-spectrum antimicrobial activity.  The nanosecond lifetime of singlet oxygen in biological media limits the diffusion of the killing radicals and thereby further localizes the cidal effect, as does the limited penetration and scattering of the activation light in human tissue. Localized alterations in cytokine flux, host-derived inflammatory mediators and bacterial virulence factors are derived from the oxidative cascade and contribute to significant anti-inflammatory effects.

Development of this technology over the past decade has been rapid, with product introductions based on various different photosensitizers in dermatology, oral medicine, immunological disorders, hospital-acquired infections, viral therapy, and other areas 1,3,4.

  1. Tardivo, J.P., et al., Methylene blue in photodynamic therapy: From basic mechanisms toclinical applications.  Photodiagnosis Photodyn Ther, 2005. 2: 175-191.
  2. Wainwright, M., Photodynamic antimicrobial chemotherapy (PACT). J Antimicrob Chemother, 1998. 42(1): p. 13-28.
  3. Dai, T. et al., Photodynamic therapy for localized infections – state of the art. Photodiagnosis Photodyn Ther. 2009. 6(3-4): 170–188.
  4. Hamblin, M.R. and T. Hasan, Photodynamic therapy: a new antimicrobial approach to infectious disease? Photochem Photobiol Sci, 2004. 3(5): p. 436-50.
  5. Andersen, R., et al., Treatment of periodontal disease by photodisinfection compared to scaling and root planing. J Clin Dent, 2007. 18(2): 34-8.
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2 Responses to “Photodynamic Disinfection (PDD) is the Antimicrobial application of PDT (aPDT)”

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