Removal Efficacy of Opportunistic Pathogens and Bacterial Community Dynamics in Two Drinking Water Treatment Trains.

Drinking water treatment processes (DWTPs) impact pathogen colonization and microbial communities in finished water; however, their efficacies against opportunistic pathogens are not fully understood. In this study, the effects of treatment steps on the removal of Legionella spp., Legionella pneumophila, nontuberculous mycobacteria, Mycobacterium avium, and two amoeba hosts (Vermamoeba vermiformis, Acanthamoeba) are evaluated in two parallel trains of DWTPs equipped with different pretreatment units. Quantitative polymerase chain reaction analysis demonstrates significantly reduced numbers of total bacteria, Legionella, and mycobacteria during ozonation, followed by a rebound in granular activated carbon (GAC) filtration, whereas sand filtration exerts an overarching effect in removing microorganisms in both treatment trains. V. vermiformis is more prevalent in biofilm (34%) than water samples (7.7%), while Acanthamoeba is not found in the two trains of DWTPs. Illumina sequencing of bacterial 16S rRNA genes reveals significant community shifts at different treatment steps, as well as distinct bacterial community structures in water and biofilm samples in parallel units (e.g., ozonation, GAC, sand filtration) between the two trains (analysis of similarities (ANOSIM), p < 0.05), implying the potential influence of different pretreatment steps in shaping the downstream microbiome. Overall, the results provide insights to mitigation of opportunistic pathogens and engineer approaches for managing bacterial communities in DWTPs.