Article Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
pubs.acs.org/est
Nontuberculous Mycobacteria in Two Drinking Water Distribution Systems and the Role of Residual Disinfection Michael B. Waak,†,‡ Timothy M. LaPara,†,§ Cynthia Halle,́ ‡ and Raymond M. Hozalski*,†,§ †
Downloaded via BUFFALO STATE on July 22, 2019 at 13:33:18 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, 500 Pillsbury Dr. SE, Minneapolis, Minnesota 55455, United States ‡ Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens veg 5, 7491 Trondheim, Norway § BioTechnology Institute, University of Minnesota, 1479 Gortner Ave., St. Paul, Minnesota 55108, United States S Supporting Information *
ABSTRACT: 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.
■
INTRODUCTION
are not reportable, so incidence may be greatly underestimated.7,9−12 NTM-related infections originate exclusively from exposure to environmental sources.7 MAC infections in individuals with HIV/AIDS are usually from contact with drinking water.13 Other disease-causing species are recovered almost exclusively from municipal water supplies.7 The increasing incidence of pulmonary infections due to NTM may be linked to the modern preference for showers over baths, with infectious cells transmitted by aerosolized tap water.14,15 Biofilms in shower heads commonly test positive for NTM species,16 but there is interest in whether premise plumbing NTM also originate from DWDS biofilms via drinking water transmission. Though water-main biofilms may harbor other opportunistic pathogens, like Legionella spp., residual chloramine may reduce their abundance.17,18 It is unclear, however, whether residual chloramine also reduces opportunistic MAC, particularly
Drinking water derived from surface waters is routinely disinfected to suppress waterborne pathogens. In the United States, residual concentrations of free chlorine (HOCl/OCl−) or chloramines (primarily monochloramine, NH2Cl) reduce microbial growth during the hours to weeks that water traverses the drinking water distribution system (DWDS). Though effective at reducing bacterial biomass within DWDS biofilms, the residual disinfectant may encourage the presence of disinfectant-tolerant microbes, particularly Mycobacterium spp.1−5 Nontuberculous mycobacteria (NTM) are defined as all environmental mycobacteria that do not cause tuberculosis or leprosy. These mycobacteria are ubiquitous in soil and water and include opportunistically pathogenic species.6 Mycobacterium avium complex (MAC), notably, is the primary cause of NTM-related disease worldwide, usually as pulmonary infection.7 Incidence ranges from 1.0 to 1.8 per 105 people among industrialized nations.7 Individuals with pulmonary disease have a poor prognosis, with a mortality rate often exceeding 25%.8 Though incidence and mortality are comparable to Legionnaires’ disease, NTM-related illnesses © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
April 1, 2019 June 24, 2019 July 9, 2019 July 9, 2019 DOI: 10.1021/acs.est.9b01945 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
with their corresponding regional or national drinking water standards. Sample collection. Water-main biofilms. Water-main sections were removed from the DWDS, as previously described.17 Briefly, the exteriors of the mains were cleaned and disinfected with a chlorine-bleach rinse (approximately 400 mg L−1 as Cl2). Soon after water shutoff (i.e.,
