Pseudomonas fluorescens is one of the first colonizers of bacterial biofilm in water systems and a member of opportunistic premise plumbing pathogens (OPPPs). The aim of this study was to examine the effect of UV light and sodium hypochlorite on the formation and destruction of mature P. fluorescens biofilm on ceramic tiles. Planktonic bacteria or bacteria in mature biofilm were exposed to UV light (254 nm) for 5, 20 s. and to 0.4 mg/L sodium hypochlorite for 1 min. Mature biofilm was also exposed to increased concentration of sodium hypochlorite of 2 mg/L for 0.5, 1 and 2 h and combined with UV. Prolonged action of sodium hypochlorite and an increase in its concentration in combination with UV gave the best results in the inhibition of biofilm formation after the pre-treatment and destruction of mature biofilm. The effect of hyperchlorination in combination with UV radiation shows better results after a long exposure time, although even after 120 min there was no completely destroyed biofilm. Furthermore, the mechanism of the effect of combined methods should be explored as well as the importance of mechanical cleaning that is crucial in combating bacterial biofilm in swimming pools.

Pool water must meet certain chemical and microbiological conditions to ensure high water quality and a safe environment for users. A recreational swimming pool treated with a combined disinfection method (chlorination and UV radiation) was monitored for 18 months. Selected chemical and microbiological parameters of the indoor freshwater pool were analyzed, and the in vivo presence of Pseudomonas aeruginosa biofilm was assessed and further correlated to the type of disinfection. P. aeruginosa isolated from biofilm was further examined to determine the effects of combined disinfection methods on the formation and destruction of mature biofilm in vitro. The in vitro application of the combined disinfection methods led to the inhibition of planktonic P. aeruginosa biofilm formation (68.9% compared to the control group) and were more effective in the partial destruction of mature biofilm than individual disinfection methods (from 25.4 to 26.3%). The obtained results indicate the better microbiological and chemical quality of pool water when combined disinfection was applied. Our results contribute to developing the optimization of pool water disinfection methods and biofilm control.