Photodynamic inactivation of staphylococci with 5-aminolaevulinic acid or photofrin

Widespread use of antibiotics for bacterial infections is a reason for antibiotic resistance. Therefore, alternatives like photodynamic therapy (PDT) are studied for bacterial eradication. The viability of Staphylococcus (S.) aureus and S. epidermidis was studied following photosensitisation with different concentrations of 6-aminolevulinic acid (5-ALA) or Photofrin(R) and irradiation with a dye laser. After ALA without irradiation growth of S. epidermidis was reduced, surprisingly growth of S. aureus significantly increased. Using ALA and light a significant and concentration-dependent decrease of bacterial growth was measured in both strains. However for S. epidermidis there was no difference between ALA with or without irradiation. Photofrin without light decreased bacterial growth significantly, indicating a high dark toxicity of the drug. Photofrin and light lead to a highly significant reduction of growth in both strains. While 5-ALA killed only up to 39% of Staphylococci, Photofrin was able to eradicate up to 93% of the bacteria. The poor response to 5-ALA may be due to an insufficient synthesis of photodynamically active porphyrins in Staphylococci. Although topical PDT could be useful, for superinfected wounds or leg ulcers, the in-vitro bactericidal effect of 5-ALA PDT on staphylococci was not satisfactory.