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-1) and a DWDS in Norway with minimal residual disinfectant (0.08 ± 0.01 mg L-1). Total mycobacteria and Mycobacterium avium complex (MAC) were quantified by qPCR targeting, respectively, atpE genes and the internal transcribed spacer region. Mycobacteria 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 diversity and consisted almost exclusively of M. gordonae. In contrast, there were various novel mycobacteria 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 also decrease mycobacterial diversity.
Bibliographical noteFunding Information:
We thank the two water utilities for providing access to their drinking water distribution systems. This work was supported primarily with a grant from the water utility in the United States. The water utility in Norway contributed additional financial resources. Collaboration between the University of Minnesota and the Norwegian University of Science and Technology was possible with funding from the Norwegian Center for International Cooperation in Education (Grant NNA-2012/10128). Kyle Sandberg and Hanna Temme assisted in water sample collection. The University of Minnesota Genomics Center sequenced the 16S rRNA and hsp65 gene amplicons and provided additional technical support. Sequence analysis was possible using resources from the Minnesota Supercomputing Institute. We thank Sara-Jane Haig for providing DNA extract of Mycobacterium avium complex for use as a positive control in qPCR.
© 2019 American Chemical Society.