ANTIBACTERIAL ACTIVITY OF HYPERICIN INCORPORATED WITH PLURONIC® P123 MICELLES AGAINST OF Staphylococcus aureus AND Salmonella TYPHIMURIUM

In Brazil, Staphylococcus aureus and Salmonella sp. were common pathogens associated with foodborne diseases outbreaks in the past 10 years. Several new strategies to control the bacterial growth in food sector have been proposed, including the Photodynamic Inactivation (PDI). This technique is based on the combination of a photosensitizing agent and light, which generates reactive oxygen species that are able to exert antimicrobial effects. Hypericin is one of the several compounds that can be used as photosensitizers in PDI; however it presents low water solubility. In this sense, the association of hypericin with Pluronics® micelles (HYP-P123) is an attractive approach to ensure greater water solubility. This study evaluated the antimicrobial effectiveness of HYP-P123, using LED as a light source, against S. aureus ATCC 25923 and Salmonella Typhimurium ATCC 14028. Aliquots of a bacterial suspension (107 CFU/mL) were incubated in the dark for 15 minutes with HYP-P123 in concentrations ranging from 0.39 to 50.0 µmol/L. Then, the samples were irradiated with an orange LED source for 15 minutes. Afterward, serial dilutions of the samples were plated on Tryptic Soy Agar (TSA) and incubated at 37 ºC for 24 hours. The effect of PDI against both bacteria was expressed as CFU/mL. For controls, bacterial cells exposed only to the photosensitizer and only to light source were evaluated. No reductions in bacterial population were observed when S. aureus was exposed only to the light source or only to photosensitizer. When the light irradiation was combined with HYP-P123 at 6.24, 12.5, 25.0 and 50.0 µmol/L there were no large reductions when compared to the control the bacterial population. On the other hand, at 0.39, 0.78, 1.56 and 3.12 µmol/L, the cell counts were decreased by 4.13, 3.81, 3.02 and 1.65 log CFU/mL, respectively. The same experiments were performed for Salmonella Typhimurium ATCC 14028; however, the bacterial population was not reduced after PDI treatment. The results obtained demonstrated that S. aureus were susceptible to PDI mediated by HYP-P123, suggesting it could be used as alternative to S. aureus control in food industry.