Antimicrobial Photodynamic Approach in the Inactivation of Viruses in Wastewater: Influence of Alternative Adjuvants.

Pathogenic viruses are frequently present in marine and estuarine waters, due to poor wastewater (WW) treatments, which consequently affect water quality and human health. Chlorination, one of the most common methods used to ensure microbiological safety in tertiarily treated effluents, may lead to the formation of toxic chemical disinfection by-products on reaction with organic matter present in the effluents. Antimicrobial photodynamic therapy (aPDT) can be a promising disinfecting approach for the inactivation of pathogens, without the formation of known toxic by-products. Additionally, some studies have reported the potentiator effect on aPDT of some compounds, such as potassium iodide (KI) and hydrogen peroxide (H2O2). In the present study, the aPDT efficiency of a PS formulation constituted of five cationic porphyrins (Form) in the inactivation of E. coli T4-like bacteriophage, a model of mammalian viruses, in different aqueous matrices with different organic matter content, was evaluated. Photoinactivation studies were performed at different concentrations of Form and in the presence of the adjuvants KI and H2O2. The results showed that the efficiency of bacteriophage photoinactivation is correlated with the Form concentration, the amount of the organic matter in WW, and the adjuvant type. Form can be an effective alternative to controlling viruses in WW, particularly if combined with H2O2, allowing to significantly reduce PS concentration and treatment time. When combined with KI, the Form is less effective in inactivating T4-like bacteriophage in WW.

Efficient photodynamic inactivation of Candida albicans by porphyrin and potassium iodide co-encapsulation in micelles.

Photodynamic inactivation of bacterial and fungal pathogens is a promising alternative to the extensive use of conventional single-target antibiotics and antifungal agents. The combination of photosensitizers and adjuvants can improve the photodynamic inactivation efficiency. In this regard, it has been shown that the use of potassium iodide (KI) as adjuvant increases pathogen killing. Following our interest in this topic, we performed the co-encapsulation of a neutral porphyrin photosensitizer (designated as P1) and KI into micelles and tested the obtained nanoformulations against the human pathogenic fungus Candida albicans. The results of this study showed that the micelles containing P1 and KI displayed a better photodynamic performance towards C. albicans than P1 and KI in solution. It is noteworthy that higher concentrations of KI within the micelles resulted in increased killing of C. albicans. Subcellular localization studies by confocal fluorescence microscopy revealed that P1 was localized in the cell cytoplasm, but not in the nuclei or mitochondria. Overall, our results show that a nanoformulation containing a photosensitizer plus an adjuvant is a promising approach for increasing the efficiency of photodynamic treatment. Actually, the use of this strategy allows a considerable decrease in the amount of both photosensitizer and adjuvant required to achieve pathogen killing.