Related Experiment Video
Updated: Oct 16, 2025
LED-Based In Vitro Screening for Assessing Photoactivable Molecules in Bacterial Photodynamic Inactivation
Published on: January 24, 2025
Empowering antimicrobial photodynamic therapy of Staphylococcus aureus infections with potassium iodide
Mafalda Bispo1, Sabrina Suhani1, Jan Maarten van Dijl1
1Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ, Groningen, The Netherlands.
Abstract:
Infections caused by the Gram-positive bacterium Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), impose a great burden on global healthcare systems. Thus, there is an urgent need for alternative approaches to fight staphylococcal infections, such as targeted antimicrobial photodynamic therapy (aPDT). We recently reported that targeted aPDT with the S. aureus-specific immunoconjugate 1D9-700DX can be effectively applied to eradicate MRSA. Nonetheless, the efficacy of aPDT in the human body may be diminished by powerful antioxidant activities. In particular, we observed that the efficacy of aPDT with 1D9-700DX towards MRSA was reduced in human plasma. Here we show that this antagonistic effect can be attributed to human serum albumin, which represents the largest pool of free thiols in plasma for trapping reactive oxygen species. Importantly, we also show that our targeted aPDT approach with 1D9-700DX can be empowered by the non-toxic inorganic salt potassium iodide (KI), which reacts with the singlet oxygen produced upon aPDT, resulting in the formation of free iodine. The targeted iodine formation allows full eradication of MRSA (more than 6-log reduction) without negatively affecting other non-targeted bacterial species or human cells. Altogether, we show that the addition of KI allows a drastic reduction of both the amount of the immunoconjugate 1D9-700DX and the irradiation time needed for effective elimination of MRSA by aPDT in the presence of human serum albumin.
Insights
Antimicrobial photodynamic therapy (aPDT) effectively kills methicillin-resistant Staphylococcus aureus (MRSA). Adding potassium iodide (KI) overcomes plasma
Area of Science:
- Biomedical science
- Photochemistry
- Microbiology
Background:
- Staphylococcus aureus, particularly MRSA, causes significant healthcare burdens.
- Antimicrobial photodynamic therapy (aPDT) is a promising alternative for treating staphylococcal infections.
- The efficacy of aPDT can be reduced by antioxidants in biological environments like human plasma.
Purpose of the Study:
- To investigate the mechanism of reduced aPDT efficacy in human plasma.
- To enhance the efficacy of targeted aPDT against MRSA in the presence of human serum albumin.
- To explore the use of potassium iodide (KI) to boost aPDT performance.
Main Methods:
- Utilized a targeted aPDT approach with the S. aureus-specific immunoconjugate 1D9-700DX.
- Investigated the role of human serum albumin in reducing aPDT efficacy.
- Assessed the effect of potassium iodide (KI) on aPDT-generated singlet oxygen and MRSA eradication.
- Evaluated the specificity of the enhanced aPDT against MRSA, other bacteria, and human cells.
Main Results:
- Human serum albumin was identified as a key factor reducing aPDT efficacy by scavenging reactive oxygen species.
- Potassium iodide (KI) enhanced aPDT by converting singlet oxygen to iodine, leading to MRSA eradication.
- Achieved over a 6-log reduction in MRSA with KI-enhanced aPDT.
- The enhanced aPDT demonstrated specificity, sparing non-targeted bacteria and human cells.
Conclusions:
- Human serum albumin antagonizes aPDT efficacy against MRSA.
- Potassium iodide (KI) is a potent enhancer for targeted aPDT, enabling MRSA elimination in plasma.
- KI-mediated aPDT significantly reduces the required immunoconjugate dose and irradiation time.
- This approach offers a more effective strategy for combating MRSA infections in vivo.
