Introduction to Antimicrobial Resistance and Klebsiella pneumoniae
As antimicrobial resistance continues to rise and the development of new antibiotics remains limited, researchers are exploring innovative methods to enhance the efficacy of existing treatments. One promising approach is antimicrobial photodynamic therapy (PDT), which has shown potential in boosting the effectiveness of current antibiotics against Klebsiella pneumoniae. This bacterium is a major cause of healthcare-associated infections worldwide, particularly in cases of nosocomial pneumonia or pneumonia associated with mechanical ventilation.
Combining Red Light and Methylene Blue
In a recent in vitro study, researchers combined red light and methylene blue with commonly used antibiotics, achieving a significant reduction in bacterial counts while lowering the necessary antibiotic concentrations. The study, published in the journal Antibiotics, demonstrated that the combination of antibiotics with photodynamic therapy could completely eradicate K. pneumoniae, a result not observed with antibiotics alone at comparable doses.
Mechanism of Action
Vanderlei Salvador Bagnato, one of the study’s authors, explained that “the light acts as a facilitator. It weakens the bacteria, allowing the antibiotic to work more effectively.” The study was conducted by researchers from the Institute of Physics of São Carlos, University of São Paulo (São Carlos, Brazil), in collaboration with Texas A&M University (United States). K. pneumoniae was chosen due to its role as a leading cause of ventilator-associated pneumonia and other severe hospital-acquired infections, which are associated with high mortality rates and increasing resistance to multiple antibiotic classes.
Challenges in Treating Resistant Infections
Due to decreased sensitivity to antibiotics, therapeutic options are limited, often requiring higher doses, potentially more toxic treatments, and prolonged hospitalization. This study aimed to enhance the performance of existing antibiotics, which could be as clinically relevant as developing new agents.
Photodynamic Therapy: A Complementary Strategy
Instead of introducing new molecules, researchers evaluated the integration of antibiotics with photodynamic therapy. This method combines three components: a photosensitizing dye, light of a specific wavelength, and oxygen. When activated by light, the dye generates reactive oxygen species that damage essential bacterial components.
Comparative Analysis of Photosensitizers
The study compared methylene blue and photodithazine, both activated by a red light-emitting diode (LED) device. Antibiotics were administered at progressively lower concentrations, either alone or in combination with photodynamic therapy. When methylene blue was paired with light, K. pneumoniae became significantly more sensitive to antibiotics, with bacterial reduction reaching up to six orders of magnitude compared to antibiotics alone.
Photodynamic Therapy as a Sensitizing Agent
Beyond its direct bactericidal effects, photodynamic therapy appears to act as a sensitizing factor. Disruption of the outer membrane of these Gram-negative bacteria may facilitate antibiotic entry and interfere with classic resistance mechanisms, including efflux pumps and molecular target alterations.
Potential and Limitations of Photodynamic Therapy
Photodynamic therapy has long been studied as an antimicrobial strategy, often considered an alternative rather than a complementary strategy to antibiotics. Experimental evidence indicates that this technique can inactivate Gram-positive and Gram-negative bacteria, fungi, viruses, and protozoa without inducing resistance, as it simultaneously causes oxidative damage to multiple cellular targets. However, most studies have evaluated the technique in isolation under controlled experimental conditions, limiting its application in clinical practice.
Review of Literature and Current Study Findings
A literature review published in 2024 identified photodynamic therapy as a promising approach for multidrug-resistant strains but highlighted the heterogeneity of study designs and the lack of data on combined treatments. The present study systematically evaluated photodynamic therapy as a bacterial sensitizer, demonstrating increased activity of ciprofloxacin, gentamicin, and ceftriaxone when used with light and methylene blue.
Implications for Gram-Negative Bacteria
These results support growing evidence that photodynamic therapy enhances antibiotic efficacy by disrupting bacterial membranes and resistance-related structures. In Gram-negative bacteria like Klebsiella, the outer membrane rich in lipopolysaccharides serves as a physical barrier limiting the penetration of many antimicrobial agents. Oxidative damage caused by photodynamic therapy can compromise this barrier, increase membrane permeability, and facilitate intracellular penetration of antibiotics targeting internal structures.
Synergy and Treatment Design
The degree of synergy varied depending on the photosensitizer and antibiotic class involved. Previous studies have reported synergistic effects between methylene blue-mediated photodynamic therapy and aminoglycosides, such as gentamicin, against Staphylococcus aureus and Pseudomonas aeruginosa. These studies indicate that oxidative damage to the membrane enhances the effects of antibiotics acting on protein synthesis by facilitating their access to bacterial ribosomes.
Challenges and Future Directions
The authors emphasized that the results were limited to in vitro experiments using standard laboratory strains. Efficacy in animal models or human infections remains unknown, particularly in deep infections where light penetration may be limited. Challenges remain in standardization, including optimal light dose, choice of photosensitizer, timing of application, and combination with antibiotics. Interactions between these variables are likely to be pathogen- and site-specific.
Potential Clinical Applications
Researchers suggested that this strategy could be particularly suited for localized infections accessible to light, such as chronic wounds, ulcers, device-associated infections, and certain respiratory conditions. With methylene blue and LED devices already used in clinical practice, the translational barrier may be less significant than that associated with developing new antimicrobial agents.
“This is a smart way to repurpose safe and well-known technologies to address one of the greatest public health challenges,” concluded Dr. Bagnato.
This article was translated from the Portuguese edition of Medscape.
🔗 **Fuente:** https://francais.medscape.com/viewarticle/lumi%C3%A8re-rouge-pourrait-elle-aider-lutter-contre-2026a10007mo