Photodynamic Inactivation of Microbial Pathogens: Disinfection of Water and Prevention of Water-Borne Diseases

Abstract

Porphyrins have been shown to act as very efficient photosensitizing agents against a broad number of microbial pathogens, including bacteria, fungi, and protozoa. This property has promising applications at a clinical level for the treatment of infectious diseases by photodynamic therapy. Moreover, this technique is also being used to address environmental problems of high significance, such as the decontamination of wastewaters, the disinfection of fish-farming tanks, the protection of animal species (e.g., amphibians and reptiles) that are endangered by pathogens whose life cycle takes place largely in aqueous media, and the control of populations of noxious insects. Such diversified applications take advantage of the availability of a truly large number of porphyrin derivatives with chemical structures that can be tailored to comply with the physical and chemical properties as well as the biological features of several milieus. In addition, the property typical of porphyrins to absorb essentially all of the wavelengths in the sun emission spectrum allows the promotion of processes largely based on natural resources with significant energy savings and low impact on ecosystems.

Potential applications of porphyrins in photodynamic inactivation beyond the medical scope

“…In addition, the potential application of PDI to destroy (micro)organisms goes beyond the medical field, with particular focus on the environmental area [28][29][30][31][32].…”

In vitro photoinactivation of bovine mastitis related pathogens

“…The antimicrobial properties from PDT combine a harmless photoactivatable dye with visible light and molecular oxygen. Its mechanism of action is based on the excitation of photosensitive (i.e., lightsensitive) substances by light at proper wavelengths, resulting in the formation of reactive oxygen species, which in turn damage subcellular structures that are fundamental to the survival of microorganisms, and so far no resistant microorganisms have been reported [16][17][18]. Factors that will determine the selective death of host cells or microbial inactivation are directly related to the affinity of photosensitive molecules used as well as to the light and chemical dosimetry applied [16].…”

Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus aureus Cells

“…An alternative method includes a non‐oncologic application of photodynamic therapy (PDT), named photodynamic inactivation of microorganism (PDI) . Although the photodynamic action was discovered over 100 years ago as a means for killing microorganisms, it was not until recent years that interest in the antimicrobial effects of PDT has been proposed as a therapy for a large variety of localized infections …”