A study of photobactericidal activity in the phenothiazinium series

The photodynamic antibacterial properties of a closely related series of commercially available phenothiazinium dyes were tested against a range of pathogenic strains of Gram-positive (Staphylococcus aureus, Enterococcus faecalis, Bacillus cereus) and Gram-negative organisms (Escherichia coli, Pseudomonas aeruginosa). The photosensitisers were illuminated using a non-laser light source at a fluence of 1.75 mW cm-2 and this resulted in the enhancement of antibacterial activity in liquid culture. In several cases, illumination resulted in considerable decreases in the minimum lethal concentrations required, giving up to 100-fold increases in bactericidal activity.