Nontuberculous Mycobacteria in Two Drinking Water Distribution Systems and the Role of Residual Disinfection.

Nontuberculous 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) and a DWDS in Norway with minimal residual disinfectant (0.08 ± 0.01 mg L). Total mycobacteria and complex (MAC) were quantified by qPCR targeting, respectively, genes and the internal transcribed spacer region. Mycobacteria concentrations in drinking water did not differ between the two systems ( = 0.09; up to 6 × 10 copies L) but were higher in the biofilms from the chloraminated DWDS ( = 5 × 10; up to 5 × 10 copies cm). MAC were not detected in either system. Sequencing of mycobacterial genes indicated that the chloraminated DWDS lacked diversity and consisted almost exclusively of . In contrast, there were various novel mycobacteria in the no-residual DWDS. Finally, - and -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 also decrease mycobacterial diversity.