Illuminating the mechanism: gene expression responses to antimicrobial photodynamic therapy

Photodynamic treatments are promising antimicrobial approaches that rely on the generation of reactive oxygen species (ROS), which lead to damage to bacterial cell structures. As the number of studies investigating gene expression changes in microorganisms following antimicrobial photodynamic inactivation (aPDI) and antimicrobial blue light (aBL) exposure is steadily increasing, there is a clear need for a comprehensive review that synthesizes these findings. This article aims to address this gap by presenting the current state of knowledge on transcriptomic alterations induced by photodynamic therapies, with a particular focus on studies utilizing qPCR and RNA-seq methodologies. Investigated genes were divided into key functional categories associated with virulence factors, DNA repair, detoxification and oxidative stress response, defense mechanisms and cellular metabolism. A general trend toward reduced expression of virulence-related genes has been observed, indicating the potential of these methods not only in eradicating bacteria but also in reducing their pathogenicity. Increased expression of certain genes linked with oxidative stress response and heat shock proteins may reflect adaptive or compensatory survival mechanisms. Differences in experimental results are often due to different protocols regarding the type of photosensitizer, wavelength of light or phase of bacterial growth.