Presence and Survival of Legionella in Drinking Water Distribution Systems

摘要

Legionella are a relevant example of a poorly understood water-born pathogen oftenrnassociated with water biofilms. These bacteria are ubiquitous in natural and artificial waterrnsupplies where protozoan host endoparasitization and biofilm association are involved in theirrnlife cycle. Humans can become incidental hosts potentially resulting in the deadly pneumoniarnLegionnaires’ Disease. Current Legionella knowledge is severely lacking in several key areas,rnparticularly concerning the interactions between the bacteria and the biofilms they colonize.rnTo further elucidate the ecology and survival of Legionella in distribution systems, threernapproaches were taken: 1) examining biofilm samples collected from water meters, 2)rninoculating a model distribution system with Legionella, and 3) assessing the survival ofrnLegionella in tap water at varying temperatures. Private residence drinking water meters wererncollected from two general locations within Central Arizona, 40 from area A and 30 from area B.rnUpon removal for repair by local city personnel, the meters were sampled within two hours.rnBiofilms were collected by scraping the inlet of each meter using nylon brushes. PCR wasrnperformed on samples using Legionella spp. 16s RNA primers and L. pneumophila mip genernprimers, followed by sequencing for confirmation. PCR positive samples were then culturedrnonto BCYE-GPCV media. Of the meter samples, 9 tested positive for Legionella (all from ArearnA) and 5 of these samples also tested positive for L. pneumophila.rnA model water distribution system was used to examine the dissemination and survival ofrnLegionella into water system. This 50L model consists of PVC and copper tubing attached to arnreservoir holding coupons for biofilm formation and circulates tap water from the city of Tempe,rnAZ. After several weeks of biofilm development, a culture of L. pneumophila was inoculatedrninto the system. Through the course of 131 days, water and biofilm samples were collected from the system and analyzed for the presence of Legionella using the techniques previouslyrndescribed. Throughout the entire course of the experiment, Legionella remained culturable inrnboth water and biofilm samples. Furthermore, complete association of Legionella with thernsystem's biofilms was not observed.rnA bench scale study was performed in which L. pneumophila cells were inoculated intorntubes containing tap and incubated at 4 and 25℃, with concentrations measured over time.rnBoth temperatures showed a steady decrease in concentrations, followed by stabilization. Thisrnoccurred almost 30 days earlier at 25℃ with final population levels nearly 3-fold higher than atrn4℃. The results provided by this study document the survival of Legionella under differentrnenvironmental conditions and provide relevant knowledge in identifying conditions whichrnpromote survival and potential growth of Legionella, information that could prove useful forrnmaintenance and monitoring procedures in drinking water distribution systems.