Photosensitising agents—circumventing resistance and breaking down biofilms: a review

While most of the current antimicrobial armamentarium is based on single mode of action drugs, it is apparent that this approach aids in the selection of resistance via target alteration, over-expression of efflux pumps, etc. Photosensitising drugs produce reactive oxygen species (ROS) on illumination and this allows non-specific attack, e.g. by singlet oxygen, at the microbial level. Singlet oxygen is very difficult to defend against, due to its high reactivity, and is known to denature antioxidant enzymes such as superoxide dismutase and catalase. Photosensitisers based on the phenothiazinium chromophore exhibit high, broad-spectrum antibacterial activity regardless of conventional drug-resistance status (e.g. against MRSA and VRE), as well as antifungal and antiviral activity. In addition, ROS produced by the photosensitisers on illumination are active against the biofilm structure itself, causing general oxidative breakdown alongside cell killing. The photoantimicrobial approach is suggested as an effective, topical method of broad-spectrum disinfection, particularly in the healthcare environment.