Muhammad Atif Nisar, Kirstin E Ross, Melissa H Brown, Richard Bentham, Giles Best, Nicholas S Eyre, Sophie C Leterme, Harriet Whiley
is the causative agent of Legionnaires' disease, and its prevalence in potable water is a significant public health issue. Water stagnation within buildings increases the risk of However, there are limited studies investigating how stagnation arising through intermittent usage affects proliferation and the studies that are available do not consider viable but non culturable (VBNC) . This study used a model plumbing system to examine how intermittent water stagnation affects both VBNC and culturable . The model plumbing system contained a water tank supplying two biofilm reactors. The model was initially left stagnant for ���5 months (147 days), after which one reactor was flushed daily, and the other weekly. Biofilm coupons, and water samples were collected for analysis at days 0, 14 and 28. These samples were analysed for culturable and VBNC , free-living amoebae, and heterotrophic bacteria. After 28 days, once-a-day flushing significantly ( < 0.001) reduced the amount of biofilm-associated culturable (1.5 log reduction) compared with weekly flushing. However, higher counts of biofilm-associated VBNC (1 log higher) were recovered from the reactor with once-a-day flushing compared with weekly flushing. Likewise, once-a-day flushing increased the population of biofilm-associated (approximately 3 log higher) compared with weekly flushing, which indicated a positive relationship between VBNC and . This is the first study to investigate the influence of stagnation on VBNC under environmental conditions. Overall, this study showed that a reduction in water stagnation decreased culturable but not VBNC .
