Persistence of Nontuberculous Mycobacteria in a Drinking Water System after Addition of Filtration Treatment

Abstract

There is evidence that drinking water may be a source of infections with pathogenic nontuberculous mycobacteria (NTM) in humans. One method by which NTM are believed to enter drinking water distribution systems is by their intracellular colonization of protozoa. Our goal was to determine whether we could detect a reduction in the prevalence of NTM recovered from an unfiltered surface drinking water system after the addition of ozonation and filtration treatment and to characterize NTM isolates by using molecular methods. We sampled water from two initially unfiltered surface drinking water treatment plants over a 29-month period. One plant received the addition of filtration and ozonation after 6 months of sampling. Sample sites included those at treatment plant effluents, distributed water, and cold water taps (point-of-use [POU] sites) in public or commercial buildings located within each distribution system. NTM were recovered from 27% of the sites. POU sites yielded the majority of NTM, with >50% recovery despite the addition of ozonation and filtration. Closely related electrophoretic groups of Mycobacterium avium were found to persist at POU sites for up to 26 months. Water collected from POU cold water outlets was persistently colonized with NTM despite the addition of ozonation and filtration to a drinking water system. This suggests that cold water POU outlets need to be considered as a potential source of chronic human exposure to NTM.

Opportunistic pathogens enriched in showerhead biofilms

“…Mycobacteria readily form biofilms and, because of their generally waxy quality, may be particularly resistant to shear forces generated in shower operation (28)(29)(30)(31)(32)(33)(34)(35)(36). Furthermore, many species of biofilm-forming mycobacteria are chlorineresistant, and thus potentially can be enriched by chlorine disinfection protocols used by many municipalities (28,29,34,37,38). Consistent with this, we only observed mycobacterial rRNA gene sequences in municipal water systems, not in untreated well water systems.…”

“…The reasons for the enrichment of mycobacteria are not clear. Mycobacteria readily form biofilms and, because of their generally waxy quality, may be particularly resistant to shear forces generated in shower operation (28)(29)(30)(31)(32)(33)(34)(35)(36). Furthermore, many species of biofilm-forming mycobacteria are chlorineresistant, and thus potentially can be enriched by chlorine disinfection protocols used by many municipalities (28,29,34,37,38).…”

Biofilms on Hospital Shower Hoses: Characterization and Implications for Nosocomial Infections

“…Their frequent occurrence in such habitats may be explained by their ability to survive stressors commonly found in distribution systems, such as oligotrophic conditions, chlorination, and hot temperatures (23,24). However, most previous surveys reporting the occurrence and prevalence of mycobacteria in DW have been restricted to 16S rRNA gene fragment analysis, lacking resolution at the species level (25), and to culturebased techniques (17,26,27), which often provide a biased repre-sentation of the sample due to the selective lab media, culture conditions, and volume of the sample processed.…”

Shared Mycobacterium avium Genotypes Observed among Unlinked Clinical and Environmental Isolates

“…Some validation is provided by the fact that multiple isolates from the same patient, either from separate anatomic sites or taken over time, often have the same fingerprint (11,12,17,21,22). When matching or highly similar fingerprints are found between patients (17,(21)(22)(23), in the same environmental source over time (22,24), or between a patient and his environment (22,23,(25)(26)(27)(28), this is often interpreted as support for a link of some sort. These kinds of matches are interpreted to indicate a shared source of acquisition, continuous colonization, or probable source of acquisition, respectively.…”