S8: Microbial Control of Recreational Waters

BACKGROUND:  Waterborne pathogens can present a health threat to bathers of recreational beaches, swimming pools, and whirlpool spas.  Consequently, effective microbial control strategies are essential to limit pathogen exposure and minimize health risk.  However, some pathogens are able to evade microbial control through innate recalcitrance or protective means such as biofilms.  METHODS AND RESULTS:  In this study, bromine disinfection of a whirlpool spa (Jacuzzi^®) was examined to understand microbial control of (1) naturally-occurring Pseudomas aeruginosa colonized in the spa and (2) fecal indicator bacteria (FIB) released from bathers.  While P. aeruginosa reached elevated levels in spa water upon bromine depletion, the bacterium was not detected by cultivation in 1-L samples following 30 minutes disinfection with a bromine “shock” dose (10 mg per L).  However, P. aeruginosa reappeared in spa waters when bromine dropped to about 1.5 mg per L.  P. aeruginosa persistence in spa surface biofilm was suggested by survival of the organism in coupon biofilms suspended in the spa dosed with10 mg per L bromine.  Control of FIB (coliforms and enterocci) released from bathers (2 or 4 for 60 minutes) was effective with bromine until disinfectant levels decreased to less than 2 mg per L during spa bathing.  CONCLUSIONS:  While bromine can effectively control planktonic P. aeruginosa in spa waters, the bacterium sequestered within surface biofilm could survive a bromine “shock” dose and reseed waters when the disinfectant diminishes.  In addition, bromine doses must accommodate bather load to maintain disinfectant residuals needed to control pathogens released from bathers.