A study on the bacterial photo-toxicity of phenothiazinium based photosensitisers

“Comet assay” showed light activated (3.15 J cm−2 over 30 min) phenothiazinium based photosensitisers (PhBPs) to induce photo-damage of Staphylococcus aureus DNA, as indicated by DNA “tails” between 80 and 120 μm. In general, PhBPs exhibited significant singlet oxygen yields (ΦΔPhBP > 0.7), suggesting the use of type II mechanisms of photo-oxidation. However, the photodynamic action of PhBPs on DNA showed generally insignificant production of 7,8-dihydro-8-oxo-2′-deoxyguanosine, normally a major product of type II DNA photo-oxidation. These combined results show DNA to be a major site of action of PhBPs and suggest that this action may involve type II attack on a nucleoside(s) other than guanosine.