Rose Bengal Conjugated to Lectins for Targeted Antibacterial Photodynamic Treatment

Due to rising antibiotic resistance, it is necessary to develop alternative ways to combat pathogenic bacteria. One alternative is photodynamic antibacterial chemotherapy (PACT). This work presents the conjugation of the photosensitizer Rose Bengal (RB) to lectins to improve its efficacy against Gram-positive and Gram-negative bacteria. Two lectins, concanavalin A (ConA) and wheat germ agglutinin (WGA), were covalently linked to RB. Spectroscopic and chromatographic data confirmed successful conjugation. Microscopic examination demonstrated that both lectins agglutinate cells of Gram-positive S. aureus, including clinical multidrug-resistant MRSA strains, and Gram-negative E. coli, P. aeruginosa, and S. paratyphi B, although ConA showed a more pronounced reaction. Photodynamic assays showed that ConA-RB achieved complete eradication of S. aureus at significantly lower concentrations and light doses than free RB or WGA-RB. ConA-RB also exhibited higher efficacy against Gram-negative bacteria compared to free RB at lower concentrations and shorter illumination periods. WGA-RB was less effective, showing preferential activity against S. aureus. Our findings suggest that lectin–RB conjugates offer a promising approach for selective antibacterial treatment under illumination.