Free-Living Amoeba and Associated Pathogenic Bacteria in Well- Chlorinated Drinking Water Storage Tanks

Free-living amoebae (FLA) and amoeba-resistant bacteria (ARB) are of increasing concern for water utilities as they cause diseases in humans. To protect consumers, disinfectants are used to prevent colonization by these pathogens in drinking water; however, FLA possess inherent defence mechanisms that can protect them from disinfection. This study investigated the presence and abundance of these amoebae and bacteria in chlorinated drinking water storage tanks in Western Australia. Viability and molecular testing methods, in the form of culturing, quantitative polymerase chain reaction, and 16S rRNA gene amplicon sequencing, were employed to detect amoebae and bacteria present in bulk water and sediment samples. FLA and ARB were detected in water storage tanks that had free chlorine residuals above 0.5 mg/L. Viable Acanthamoeba spp. and Vermamoeba sp. were isolated from the tanks along with various other FLA also detected molecularly. Nontuberculous mycobacteria, a known ARB and opportunistic pathogen, was isolated from all tanks and sample types as well as in the growth fronts of the viable amoebae. This study illustrates the presence and persistence of FLA, ARB, and associated bacterial communities in well-chlorinated water storage tanks, highlighting the need for continued surveillance and risk management.