Application of Response Surface Methodology to Evaluate Photodynamic Inactivation Mediated by Eosin Y and 530 nm LED against Staphylococcus aureus.

Photodynamic antimicrobial chemotherapy (PAC) is an efficient tool for inactivating microorganisms. This technique is a good approach to inactivate the foodborne microorganisms, which are responsible for one of the major public health concerns worldwide-the foodborne diseases. In this work, response surface methodology (RSM) was used to evaluate the interaction of Eosin Y (EOS) concentration and irradiation time on Staphylococcus aureus counts and a sequence of designed experiments to model the combined effect of each factor on the response. A second-order polynomial empirical model was developed to describe the relationship between EOS concentration and irradiation time. The results showed that the derived model could predict the combined influences of these factors on S. aureus counts. The agreement between predictions and experimental observations (R2adj = 0.9159, p = 0.000034) was also observed. The significant terms in the model were the linear negative effect of photosensitizer (PS) concentration, followed by the linear negative effect of irradiation time, and the quadratic negative effect of PS concentration. The highest reductions in S. aureus counts were observed when applying a light dose of 9.98 J/cm2 (498 nM of EOS and 10 min. irradiation). The ability of the evaluated model to predict the photoinactivation of S. aureus was successfully validated. Therefore, the use of RSM combined with PAC is a promising approach to inactivate foodborne pathogens.

The Remarkable Effect of Potassium Iodide in Eosin and Rose Bengal Photodynamic Action against Salmonella Typhimurium and Staphylococcus aureus.

Antimicrobial photodynamic therapy (aPDT) has been shown as a promising technique to inactivate foodborne bacteria, without inducing the development of bacterial resistance. Knowing that addition of inorganic salts, such as potassium iodide (KI), can modulate the photodynamic action of the photosensitizer (PS), we report in this study the antimicrobial effect of eosin (EOS) and rose bengal (RB) combined with KI against Salmonella enterica serovar Typhimurium and Staphylococcus aureus. Additionally, the possible development of bacterial resistance after this combined aPDT protocol was evaluated. The combination of EOS or RB, at all tested concentrations, with KI at 100 mM, was able to efficiently inactivate S. Typhimurium and S. aureus. This combined approach allows a reduction in the PS concentration up to 1000 times, even against one of the most common foodborne pathogenics, S. Typhimurium, a gram-negative bacterium which is not so prone to inactivation with xanthene dyes when used alone. The photoinactivation of S. Typhimurium and S. aureus by both xanthenes with KI did not induce the development of resistance. The low price of the xanthene dyes, the non-toxic nature of KI, and the possibility of reducing the PS concentration show that this technology has potential to be easily transposed to the food industry.