Synergistic bactericidal effects of photodynamic inactivation technology combined with citric acid on staphylococcus aureus

This study focuses on the inactivation efficiency and mechanism of curcumin-mediated Photodynamic Inactivation Technology (PDI) enhanced by citric acid against Staphylococcus aureus . The inactivation effect of PDI on Staphylococcus aureus was assessed using a colony counting method, morphological changes were observed via scanning electron microscopy (SEM), and the levels of reactive oxygen species (ROS) and the activities of catalase (CAT), superoxide dismutase (SOD), adenosine triphosphatase (ATPase), and alkaline phosphatase (AKP) were measured using a microplate reader. Additionally, the degree of DNA damage was analyzed through agarose gel electrophoresis. The results demonstrated that with increasing curcumin concentration, extended illumination time, and the addition of 0.5 mg/mL citric acid, the bactericidal effect of PDI on Staphylococcus aureus was significantly enhanced ( P < 0.05). When Staphylococcus aureus was treated with 2 μmol/L curcumin combined with 0.5 mg/mL citric acid and exposed to light for 2 minutes, the total colony count in PBS decreased to 0.01% of the initial value. The photosensitizer curcumin, activated by blue light, generated highly oxidative ROS, leading to a rapid increase in ROS levels within the bacterial cells, reduced activity of intracellular antioxidant enzymes (CAT, SOD), decreased ATPase activity, increased AKPase activity in the supernatant, severe bacterial deformation, and the fading or disappearance of DNA bands, ultimately resulting in cell death. Therefore, curcumin-mediated PDI exhibits a significant inactivation effect on Staphylococcus aureus , with the synergistic effect of citric acid being particularly prominent. • Significant Synergistic Effect: PDI with citric acid achieves 99.99% Staphylococcus aureus inactivation. • Increased ROS Levels: Combined PDI and citric acid boost ROS production, enhancing bactericidal action. • Notable Structural Damage: PDI with citric acid causes severe cell deformation and reduced enzyme activity. • Increased DNA Damage: High-concentration curcumin and citric acid combined PDI lead to significant DNA degradation. • Reduced Antioxidant Enzyme Activity: PDI with citric acid lowers CAT and SOD activity, weakening bacterial defenses.