Effects of ultraviolet irradiation on biofilm formation of Pseudomonas aeruginosa

Abstract

 Major component of biofilm is known as extracellular polymeric substances (EPSs) that is produced by microorganisms to survive under various stresses, and it causes problems such as water quality deterioration and pipe corrosion in the water supply system. Ultraviolet (UV) radiation is one of the practical methods to disinfect water, and UV is one of stress factors for bacteria. In this study, the effects of ultraviolet irradiation to bacteria on the subsequent biofilm formation were evaluated. The experimental samples were prepared by mixing UV irradiated and non-irradiated suspensions of Pseudomonas aeruginosa at different ratios, which were then cultured in the microtiter plates to grow biofilms. Amount of biofilm was quantified by crystal violet staining, and metabolic activity of bacteria in the microtiter wells was determined by the adenosine triphosphate (ATP) assay. ATP in the sample containing 100 % of UV irradiated bacteria was decreased by 97 % within first 6 hours after UV exposure, and biofilm growth was subsequently observed. Furthermore, it was estimated that the biofilm growth rate in the 100 % UV-irradiated samples was more than twice of that in the sample of 0 % UV-irradiated samples. These results suggest thatUV-inactivated bacteria stimulated the intact bacteria to produce biofilms and thus indirectly contributed to promote biofilm formation in water supply systems.