The toxicities of several aminoacridines were measured against pathogenic strains of both Gram-positive (Staphylococcus aureus, Enterococcus faecalis, Bacillus cereus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) organisms. In several cases, illumination at a light dose of 6.3 J/cm 2 resulted in considerable decreases in the minimum lethal drug concentrations required, giving up to 50-fold increases in bactericidal activity. Derivatives of 9-aminoacridine (aminacrine) exhibited

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... hototoxicity against one or more of the test organisms, but the established photosensitizing acridines proflavine and acridine orange were photobactericidal against all strains.