Lectin–Rose Bengal Conjugates for Targeted Photodynamic Inactivation of Pathogenic Bacteria

The growing threat of antibiotic-resistant bacteria necessitates the development of alternative antimicrobial strategies. This study investigated the design and evaluation of novel photodynamic agents based on Rose Bengal (RB) conjugated to two plant lectins, <i>Pisum sativum</i> agglutinin (PSA) and <i>Laburnum anagyroides</i> agglutinin (LABA), for targeted photodynamic inactivation of Gram-positive and Gram-negative bacteria. Both conjugates demonstrated high singlet oxygen quantum yields compared with free RB. Antibacterial efficacy was assessed against methicillin-sensitive and methicillin-resistant <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>, and <i>Salmonella paratyphi</i> B under white LED illumination. PSA-RB exhibited superior bactericidal activity against all strains, whereas LABA-RB showed strain-specific efficacy, particularly against Gram-negative species. A binary mixture of PSA-RB and LABA-RB synergistically inactivated both MSSA and MRSA at RB concentrations of 6-10 nM and light doses of 3.1-7.8 J/cm². Complete killing of <i>E. coli</i> and <i>S. paratyphi</i> B was achieved at approximately half the RB concentrations needed for individual conjugates. PSA-RB activity primarily drove the inactivation of <i>P. aeruginosa</i>. Uptake studies revealed significantly enhanced accumulation of lectin-conjugated RB compared to free RB, with synergistic uptake observed for the conjugate mixture. These results suggest that lectin-based RB conjugates are effective antibacterial agents for photodynamic treatment, especially via the dual-targeting method.