Sensitivity of bacteria to photodynamic chemotherapy

Increasing widespread resistance of microbial cells to antibiotics raises a need to develop novel antibacterial technologies. One of the approaches that may lead to improved antimicrobial treatment and replace or least significantly reduce the use of antibiotics is photodynamic chemotherapy. This technique includes visible light excitation of nontoxic components - photosensitizers, which transfer energy to molecular oxygen, resulting in the production of reactive oxygen species that in turn cause irreversible damage to cellular components of bacteria. Photodynamic chemotherapy has been extensively studied towards both Gram-positive and Gram-negative bacteria, including antibiotic-resistant strains. Gram-positive and Gram-negative bacteria react differently to photodynamic chemotherapy, at that the former exhibit high sensitivity to the treatment. Gram-negative bacteria are less susceptible to photodynamic chemotherapy due to the presence of phospholipids, complex lipoproteins and polysaccharides in the additional outer cell envelope. From the numerous studies on the effect of photodynamic chemotherapy on different microorganisms no development of bacterial resistance to photosensitizers has been reported so far. Excitation of photosensitizers in the process of bacterial eradication can be performed by several methods, including illumination with external light sources, chemiluminescent illumination and sonodynamic activation. The two latter techniques enable to deliver photodynamic treatment without external illumination in the dark, which opens prospects for combating internal infections that are difficult or not available for treatment by traditional photodynamic chemotherapy. This property turns these techniques into promising novel antimicrobial therapeutic strategies.