Phototoxicity assessment of drugs and cosmetic products using E. coli

A gram negative bacteria Escherichia coli (Dh5α strain) was developed as an alternate test system of phototoxicity. Eight drugs (antibiotics) and cosmetic products (eight face creams) were examined for their phototoxicity using this test system. Five known phototoxic compounds were used to validate the test system. UVA-radiation induced phototoxicity of these compounds was tested by agar gel diffusion assay. Decrease in colony forming units (CFU) was taken as an end point of phototoxicity. The phototoxic compounds and antibiotics produced significant reduction in CFU (p < 0.001) at 80 μg/ml concentrations under exposure to UVA-radiation (5.4–10.8 J/cm2). One face cream was found phototoxic and produced significant decrease in CFU of E. coli at 1.0 mg/ml concentration under UVA exposure (10.8 J/cm2). The minimum effective concentration of tetracycline and dose of UVA-radiation were also determined by observing growth inhibition of E. coli through disc diffusion assay. The observations suggested that E. coli can be used as an alternative test system for phototoxicity evaluation of chemicals. A battery of test systems is required to conclude the toxic/phototoxic potential of a chemical agent. In view of the speed, easiness, sensitivity and low cost, E. coli is introduced as one of the alternate test system for phototoxicity studies in safety evaluation of various chemical ingredients or formulations used in cosmetics and drugs.