Photodynamic antimicrobial activity of hypocrellin A

Antimicrobial photodynamic therapy is a recently developed therapeutic option that combines a non-toxic photosensitizer with harmless visible light to damage the microbial cell. Hypocrellin A (HA), a natural occurring lipid-soluble perylenequinone pigment, has gained considerable interest since its anticancer and antiviral activities have been reported. Here, we examined the antimicrobial activity of HA against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli, Salmonella typhimurium). The results indicate that HA has a photodynamic antimicrobial activity against both Gram-positive and Gram-negative bacteria when CaCl2 or MgCl2 was employed. A loose binding has been established between HA and the organisms. Molecular oxygen is significantly involved in the photodynamic action of HA. Furthermore, HA maintains a photodynamic activity in terms of both types I and II reactions. Our results confirm the potential of HA to be used as a photosensitizer in antimicrobial photodynamic therapy.