The effects of iodine radicals generated via Photodynamic Inactivation with potassium iodide

Photodynamic Inactivation (PDI) has been intensively investigated as an approach against microorganisms. To enhance PDI's effectiveness, the use of potassium iodide (KI) with photosensitizers has been explored. This study evaluated the mechanisms involved in KI's enhancement of PDI. First, the photodegradation study with methylene blue (MB) with and without KI showed that KI accelerates the degradation of the photosensitizer and promotes iodine radicals generation during PDI. Antimicrobial evaluations demonstrated that PDI+KI eradicated Pseudomonas aeruginosa and Staphylococcus aureus biofilms. Iodine radicals were confirmed to be responsible for the inactivation, as both bacterial were susceptible to iodine generated through electrolysis. When the photobleaching of MB+KI was performed in low oxygen condition, the MB degradation was similar to the MB without KI. Then, singlet oxygen is crucial to produce iodine radicals. In conclusion, the iodine radicals generated via PDI with KI was responsible for the bacterial killing and offers a potent antimicrobial strategy.