Antimicrobial Photodynamic Inactivation of Pseudomonas aeruginosa Using Chlorophyllin

Antimicrobial resistance (AMR) remains a global challenge. One of the leading pathogens contributing to the burden of AMR in 2019 and the priority target for the development of alternative antimicrobial agents is the opportunistic pathogen Pseudomonas aeruginosa. One of the promising antimicrobial strategies is antimicrobial photodynamic inactivation (aPDI). Yet, many photosensitizers are tested versus planktonic cells, which fails to mirror the real-life presence of biofilms. This study investigates the efficacy of chlorophyllin (CHL) exposed to red light alone and in combination with the cationic permeabilizer polyethylenimine (PEI) or the activator of mechanosensitive channels butylparaben (BP) against different physiological states of P. aeruginosa, including planktonic cells, persister cells and biofilms. Antimicrobial susceptibility tests were performed using the broth microdilution checkerboard method to determine the bactericidal concentrations. Serine hydroxamate was used for the induction of persister cells via amino acid starvation. Dark conditions were non-lethal to P. aeruginosa. However, under illumination, CHL effectively eradicated P. aeruginosa biofilm cells in colony biofilm. Persister cells exhibited more sensitivity to CHL/PEI combinations compared to growing cells; whereas they were less sensitive to CHL/BP combinations. Neither PEI, BP nor red light alone was lethal to P. aeruginosa under the tested conditions. Visual evidence from confocal and TEM images illustrates the influence of CHL and red light, which intensifies when combined with BP. These findings highlight the potential antimicrobial effect of CHL against P. aeruginosa biofilms and enhanced strategies for targeting persister cells. Further research is needed to optimize treatment parameters and evaluate its applicability.