Synergistic effect of porphyrin-induced photodynamic antimicrobial chemotherapy combined with Gentamicin against clinically important gram-positive and gram-negative bacteria

Infectious diseases remain a major cause of death globally, particularly in developing countries, with antibiotic resistance exacerbating the issue. To address this, alternative treatments like Photodynamic Antimicrobial Chemotherapy (PACT) using porphyrins as photosensitizers are gaining attention. This study investigates the antibacterial activity of a free base porphyrin and its zinc, indium, and gallium metal conjugates, both independently and in combination with gentamicin (GEN), against gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The porphyrins and their conjugates were synthesized and characterized via UV-Vis spectroscopy, NMR, mass spectrometry, and FTIR. Photophysical properties, such as singlet oxygen and fluorescence quantum yields, were also determined. The indium metallated porphyrin showed the highest singlet oxygen yield ([Formula: see text]) (0.32) and excellent photodynamic activity, eradicating bacteria at sub-lethal light doses. The combination of PACT and GEN notably enhanced antibacterial efficacy, with the porphyrin P-InCl combined with GEN showing significant inhibition zones: 41.3 mm for S. aureus, 34.0 mm for E. coli, and 34.8 mm for P. aeruginosa, compared to GEN alone. This demonstrates the synergistic effect of combining PACT with antibiotics, significantly improving bacterial reduction compared to individual treatments. The study highlights the potential of this combination therapy as an effective strategy against antibiotic-resistant infections.