Assessing 5-Aminolevulinic Acid as a Natural Biocide Precursor for Light-Activated Eradication of Pseudomonas spp.

Photodynamic inactivation (aPDI) involves the interaction of three components: non-toxic photosensitizer molecules (PS), low-intensity visible light, and molecular oxygen. This interaction leads to the generation of toxic reactive oxygen species. The present work demonstrated the efficacy of light-induced antimicrobial photodynamic inactivation against <i>Pseudomonas aeruginosa</i> and <i>Pseudomonas putida</i> using 5-aminolevulinic acid (5-ALA) as a prodrug to produce the photosensitizer protoporphyrin IX. The photoeradication efficiency of these pathogens under blue (405 nm; 45 mW cm^-2) and red (635 nm; 53 mW cm^-2) light was investigated. Results showed that at least 30 min of blue light irradiation was necessary to achieve a 99.999% reduction of <i>P</i>. <i>aeruginosa</i>, whereas red light was less effective. <i>P. putida</i> exhibited limited susceptibility under similar conditions. To enhance aPDI efficiency, exogenous glucose was added alongside 5-ALA, which significantly increased the photodynamic efficacy-particularly against <i>P. aeruginosa</i>-leading to complete eradication after just 5 min of exposure. Spectroscopic analyses confirmed that glucose increased the levels of protoporphyrin IX, which correlated with enhanced photodynamic efficacy. Furthermore, multiple aPDI exposure reduced key virulence factors, including alkaline protease activity, biofilm formation, and swarming motility (in <i>P. aeruginosa</i>). These findings suggest that 5-ALA-mediated photodynamic inactivation offers a promising strategy to improve efficacy against resistant Gram-negative pathogens.