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Antimicrobial Photodynamic Activity of the Zn(II) Phthalocyanine RLP068/Cl Versus Antimicrobial-Resistant Priority
Ilaria Baccani1,2, Sara Cuffari1,2, Francesco Giuliani3
1Department of Experimental and Clinical Medicine (DMSC), University of Florence, Largo Brambilla, 3, 50134 Florence, FI, Italy.
Abstract:
The emergence and spread of antimicrobial resistance among pathogens are significantly reducing available therapeutic options, highlighting the urgent need for novel and complementary treatment strategies. Antimicrobial photodynamic therapy (aPDT) is a promising alternative approach that can overcome antimicrobial resistance through a multitarget mechanism of action, exerting direct bactericidal and fungicidal effects with minimal risk of resistance development. Although aPDT has shown efficacy against a variety of pathogens, data on its activity against large collections of clinical multidrug-resistant strains are still limited. In this study, we assessed the antimicrobial activity of the photosensitizer RLP068/Cl combined with a red light-emitting LED source at 630 nm (Molteni Farmaceutici, Italy) against a large panel of Gram-negative and Gram-positive bacterial strains harboring relevant resistance traits and Candida species. Our results demonstrated the significant microbicidal activity of RLP068/Cl against all of the tested strains regardless of their resistance phenotype, with particularly prominent activity against Gram-positive bacteria (range of bactericidal concentrations 0.05-0.1 µM), which required significantly lower exposure to photosensitizer compared to Candida and Gram-negative species (range 5-20 µM). Overall, these findings support the potential use of RLP068/Cl-mediated aPDT as an effective therapeutic strategy for the management of localized infections caused by MDR organisms, particularly when conventional therapeutic options are limited.
Insights
Antimicrobial photodynamic therapy (aPDT) using RLP068/Cl shows potent activity against multidrug-resistant bacteria and Candida species. This approach offers a promising strategy for treating infections where conventional therapies fail.
Area of Science:
- Microbiology
- Photomedicine
- Antimicrobial Resistance
Background:
- Antimicrobial resistance (AMR) is a growing global health threat, limiting treatment options.
- Novel therapeutic strategies are urgently needed to combat resistant pathogens.
- Antimicrobial photodynamic therapy (aPDT) offers a multitarget mechanism with low resistance development risk.
Purpose of the Study:
- To evaluate the antimicrobial efficacy of RLP068/Cl-mediated aPDT against a large panel of clinical multidrug-resistant (MDR) strains.
- To assess the activity against Gram-negative bacteria, Gram-positive bacteria, and Candida species.
- To determine the potential of RLP068/Cl-mediated aPDT as a treatment for MDR infections.
Main Methods:
- Tested the photosensitizer RLP068/Cl combined with a 630 nm red LED light source.
- Evaluated activity against a diverse collection of clinical multidrug-resistant bacterial and Candida strains.
- Determined the range of bactericidal concentrations (RCs) for different microbial types.
Main Results:
- RLP068/Cl-mediated aPDT demonstrated significant microbicidal activity against all tested strains, irrespective of resistance phenotype.
- Potent activity was observed against Gram-positive bacteria (RCs 0.05-0.1 µM).
- Lower concentrations were required for Gram-positive bacteria compared to Candida and Gram-negative species (RCs 5-20 µM).
Conclusions:
- RLP068/Cl-mediated aPDT is effective against a broad spectrum of MDR clinical isolates.
- This therapy shows particular promise for Gram-positive bacterial infections.
- aPDT represents a viable therapeutic option for localized MDR infections, especially when standard treatments are ineffective.
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