Persistence of specialized bacteria during disinfectant challenge in a new swimming pool

• Disinfection significantly and temporarily simplified bacterial community in a new swimming pool • Environmental bacteria possessing specialized metabolic capabilities or harboring specialized plasmids can persist under disinfectant exposure. • A new complex Class I integron was found in Acinetobacter lwoffii Swimming pools represent a unique aquatic environment, with continuous bacterial inoculation from swimmers and high disinfectant levels to control microbial growth. Whether, how, and which groups of bacteria can survive this strong disinfectant stress and pose a potential threat to swimmer health remain poorly understood. This study leveraged the unique opportunity of a newly opened swimming pool to address these questions. Analysis of bacterial community structures in water revealed that disinfectants substantially and temporarily simplified bacterial communities, with only a few dominant specialized groups surviving under disinfectant stress. Among the culturable pathogens, such as Escherichia coli, Staphylococcus , and Acinetobacter , only specific strains possessing genetic adaptations, such as stress-tolerant plasmids, persisted. Although most of the isolated strains did not exhibit high levels of antibiotic resistance, the presence of resistant pathogens was confirmed, one of which carried a unique complex Class I integron. This study demonstrates how bacteria emerge and persist in heavily managed, disinfected aquatic environments, such as swimming pools. Consequently, there is an urgent need to shift focus from merely reducing bacterial populations to developing sustainable strategies for managing persistent bacteria to protect public health.