Sustainable water treatment in aquaculture – photolysis and photodynamic therapy for the inactivation of Vibrio species

Species of the genus Vibrio have been recognized as one of the most significant pathogens in aquaculture farming, causing mass mortality of farmed stocks. Photodynamic Antimicrobial Chemotherapy (PACT) with singlet oxygen (¹O₂) has been identified as a powerful and sustainable water treatment method for pathogen eradication. In this study, the efficiencies of photolytic and photodynamic disinfection protocols were studied with two Vibrio species, Vibrio parahaemolyticus and Vibrio owensii. The selected microorganisms were successfully cultivated in marine broth and irradiations were performed with ~10⁸ bacteria mL⁻¹. Treated samples were monitored for bacterial regrowth for up to 7 days. Photolysis experiments were initially conducted with UV-A, UV-B for up to 2 h and visible (VIS) light for up to 24 h. Of these, only irradiation with UV-B light for at least 45 min was efficient in controlling Vibrio. Irradiations with VIS light were subsequently repeated under PACT conditions in dose−response experiments with two water-soluble porphyrins, [T₄(MePy)P] and [TPPS₄]. Disinfections of samples were successful for both porphyrin types at minimum concentrations of 10 μM and 24 h of irradiation.