Effect of ultraviolet (UV) radiation on the abundance and respiration rates of probiotic bacteria

Effects of ultraviolet radiation (UV) on probiotic bacteria (Bacillus subtilis and B. licheniformis) were tested in two experiments, with the following treatments: (i) UV treatment using fluorescent and UV-lamps and (ii) Control CTRL, using fluorescent lamps. Bacterial abundance and respiration were evaluated every 24h for 3days for Experiment 1, and at 0, 6 and 24h for Experiment 2. In the Experiment 1, total UV dose was 4336.41mWcm-2. UV treatment presented small respiration rates only on day 3, while in the CTRL oxygen consumption was always high. On all days, the abundance of the Bacilli exposed to UV was significantly smaller than that of the CTRL. The second experiment, with total UV dose of 1445.47mWcm-2, presented oxygen consumption in the UV treatment only during the first 6h. In the CTRL, oxygen consumption increased from the beginning due to the bigger abundance Bacilli cells. Small coccus-shaped bacteria ocurred in the UV treatment of both experiments. It may be concluded that exposure to UV, normally used for water disinfection, can inactivate probiotic bacteria.