NontuberculousMycobacteria in Two Drinking WaterDistribution Systems and the Role of Residual Disinfection

Non-tuberculous mycobacteria (NTM) are frequently found in chloraminated drinking water distribution systems (DWDSs) due to their chloramine tolerance. NTM were investigated in the water-main biofilms and drinking water of a chloraminated DWDS in the United States (initial chloramine residual = 3.8±0.1 mg L −1 ) and a DWDS in Norway with minimal residual disinfectant (0.08±0.01 mg L −1 ). NTM and Mycobacterium avium complex (MAC) were quantified by qPCR targeting, respectively, atpE genes and the internal transcribed spacer region. NTM concentrations in drinking water did not differ between the two systems ( P = 0:09; up to 6×10 4 copies L −1 ) but were higher in the biofilms from the chloraminated DWDS ( P = 5×10 −9 ; up to 5×10 6 copies cm −2 ). MAC were not detected in either system. Sequencing of mycobacterial hsp65 genes indicated that the chloraminated DWDS lacked NTM diversity and consisted almost exc...