LAUSR

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 6×104 copies L-1) but were higher in the biofilms from the chloraminated DWDS (P = 5×10-9; up to 5×106 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 exclusively of M. gordonae. In contrast, there were many novel NTM species in the no-residual DWDS. Finally, Mycobacterium- and Methylobacterium-like 16S rRNA genes were often detected simultaneously, though without correlation as previously observed. We conclude that, though residual chloramine may increase mycobacterial biomass in a DWDS, it may decrease NTM diversity.