On-site filtrationof large sample volumes improves the detection of opportunistic pathogens in drinking water distribution systems

In this study, we compared conventional vacuum filtrationof small volumes through disc membranes (effective sample volumes for potable water: 0.3-1.0 L) withfiltrationof high volumes using ultrafiltration(UF) modules (effectivesample volumes for potable water: 10.6-84.5 L) for collecting bacterial biomass from raw, finished,and tap water at seven drinking water systems. Total bacteria, Legionella spp., Legionella pneumophila, Mycobacterium spp., and Mycobacterium avium complex in these samples were enumerated using both conventional quantitative PCR (qPCR) and viability qPCR (using propidium monoazide). In addition, PCR-amplifiedgene fragments were sequenced for microbial community analysis. The frequency of detection (FOD) of Legionella spp. in finishedand tap water samples was much greater using UF modules (83% and 77%, respectively) than disc filters(24% and 33%, respectively). The FODs for Mycobacterium spp. in raw, finished,and tap water samples were also consistently greater using UF modules than disc filters.Furthermore, the number of observed operational taxonomic units and diversity index values for finishedand tap water samples were often substantially greater when using UF modules as compared to disc filters.Conventional and viability qPCR yielded similar results, suggesting that membrane-compromised cells represented a minor fraction of total bacterial biomass. In conclusion, our research demonstrates that large-volume filtrationusing UF modules improved the detection of opportunistic pathogens at the low concentrations typically found in public drinking water systems and that the majority of bacteria in these systems appear to be viable in spite of disinfection with free chlorine and/or chloramine.