Microbial biofilms are responsible for a variety of microbial infections in different parts of the body, such as urinary tract infections, catheter infections, middle-ear infections, gingivitis, caries, periodontitis, orthopedic implants, and so on. The microbial biofilm cells have properties and gene expression patterns distinct from planktonic cells, including phenotypic variations in enzymic activity, cell wall composition and surface structure, which increase the resistance to antibiotics and other antimicrobial treatments. There is consequently an urgent need for new approaches to attack biofilm-associated microorganisms, and antimicrobial photodynamic therapy (aPDT) may be a promising candidate. aPDT involves the combination of a nontoxic dye and low-intensity visible light which, in the presence of oxygen, produces cytotoxic reactive oxygen species. It has been demonstrated that many biofilms are susceptible to aPDT, particularly in dental disease. This review will focus on aspects of aPDT that are designed to increase efficiency against biofilms modalities to enhance penetration of photosensitizer into biofilm, and a combination of aPDT with biofilm-disrupting agents.

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Photodynamic therapy consists of the uptake of a photosensitizing dye, often a porphyrin, by tumor tissue and subsequent irradiation of the tumor with visible light of an appropriate wavelength matched to the absorption spectrum of the photosensitizing dye. This class of molecules produces reactive oxygen species when activated by light, resulting in a direct or indirect cytotoxic effect on the target cells. Photodynamic therapy has been used in the treatment of cancer but the technology has a potential for the treatment of several disease conditions mainly because of its selectivity. However, it is not clear why the porphyrins are retained preferentially by abnormal tissue. This paper describes a study of the effect of the association of porphyrin and visible light on two mouse fibroblast cell lines: A31, normal cells and B61, an EJ-ras transformed variant of A31. Two water-soluble porphyrins were used, a positively charged one, tetra(N-methyl-4-pyridyl)porphyrin chloride, and a negatively charged one, tetra(4-sulfonatophenyl)porphyrin-Na salt (TPPS 4 ) in order to assess the effect on cell survival. The results suggest that the B61 cell line is more sensitive to incubation with the anionic porphyrin (TPPS 4 ) followed by light irradiation and that the anionic porphyrin is more efficient in killing the cells than the cationic porphyrin.

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Using three haematoporphyrin based photosensitizers we investigated their properties related to the phototransformation in solution, the inhibitory concentration (IC50) in cell culture and the threshold dose (D th ) in rat livers. The observation of such properties shows the existence of a strong correlation among them. The photosensitizer with the highest phototransformation rate is also the one with the lowest D th and IC50, showing more efficacy in cell killing and tissue necrosis during photodynamic therapy applications. We discuss this explanation for such correlation and the possible practical applications for this property. Threshold dose, J/cm 3The photostability parameter (η) versus the threshold dose (D TH ) for the three photosensitizers.

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