Abstract
BackgroundPhotodynamic antimicrobial chemotherapy (PACT) combines light, a light-absorbing molecule that initiates a photochemical or photophysical reaction, and oxygen. The combined action of these three components originates reactive oxygen species that lead to microorganisms' destruction. The aim was to evaluate the efficiency of PACT on Vibrio fischeri: 1) with buffer solution, varying temperature, pH, salinity and oxygen concentration values; 2) with aquaculture water, to reproduce photoinactivation (PI) conditions in situ.Methodology/Principal FindingsTo monitor the PI kinetics, the bioluminescence of V. fischeri was measured during the experiments. A tricationic meso-substituted porphyrin (Tri-Py+-Me-PF) was used as photosensitizer (5 µM in the studies with buffer solution and 10–50 µM in the studies with aquaculture water); artificial white light (4 mW cm−2) and solar irradiation (40 mW cm−2) were used as light sources; and the bacterial concentration used for all experiments was ≈107 CFU mL−1 (corresponding to a bioluminescence level of 105 relative light units - RLU). The variations in pH (6.5–8.5), temperature (10–25°C), salinity (20–40 g L−1) and oxygen concentration did not significantly affect the PI of V. fischeri, once in all tested conditions the bioluminescent signal decreased to the detection limit of the method (≈7 log reduction). The assays using aquaculture water showed that the efficiency of the process is affected by the suspended matter. Total PI of V. fischeri in aquaculture water was achieved under solar light in the presence of 20 µM of Tri-Py+-Me-PF.Conclusions/SignificanceIf PACT is to be used in environmental applications, the matrix containing target microbial communities should be previously characterized in order to establish an efficient protocol having into account the photosensitizer concentration, the light source and the total light dose delivered. The possibility of using solar light in PACT to treat aquaculture water makes this technology cost-effective and attractive.
Highlights
Aquaculture is an important and rapidly growing industry of intensive seafood production that contributes to global supplies of fish, crustaceans and molluscs [1]
This study aimed to evaluate a) the influence of the pH, temperature, salinity, and oxygen concentration on the PI of the light emitting Gram-negative bacterium Vibrio fischeri under controlled experimental conditions, and b) how the PI of V. fischeri is affected by using aquaculture water samples, under artificial white light and solar light
Photoinactivation assays in buffer solution In order to evaluate the influence of the pH, temperature, salinity and oxygen concentration on the PI of V. fischeri, light and dark controls were carried out for all the experiments including for each value of the variables
Summary
Aquaculture is an important and rapidly growing industry of intensive seafood production that contributes to global supplies of fish, crustaceans and molluscs [1] It has grown faster than all other food animal-producing sectors. The use of large amounts of a wide variety of antibiotics, including nonbiodegradable ones, results in their accumulation in the aquatic environment which exerts a selective pressure for long periods of time [12] This process has raised several problems: a) the emergence of antibiotic-resistant bacteria in aquaculture environments; b) the increase of antibiotic resistance in fish pathogens; c) the transfer of these resistance determinants to bacteria of land animals and to human pathogens; and d) in alterations of the bacterial flora both in sediments and in water column [12]. The aim was to evaluate the efficiency of PACT on Vibrio fischeri: 1) with buffer solution, varying temperature, pH, salinity and oxygen concentration values; 2) with aquaculture water, to reproduce photoinactivation (PI) conditions in situ
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