Bacteroides Survival and Growth in Drinking Water Distribution Systems

摘要

Bacteroides are the predominant bacterial group in the complex intestinal flora of almostrnall mammals and have been suggested as alternative indicators of fecal pollution since they arernhighly abundant in feces and are thought to have limited potential to grow in environment. Inrnrecent years Bacteroides have also been the focus of numerous microbial source tracking studies,rnin part because they are known to have a high degree of host specificity that likely reflectsrndifferences in source animal digestive systems. The use of Bacteroides spp. as indicatorrnorganisms, however, has been hindered by the complex cultivation conditions required. Thernintroduction of molecular methods has made it possible to detect bacterial species that belong tornthe order Bacteroidales, an order that includes the genus Bacteroides, without cultivation.rnHowever, despite the potential of Bacteroides as a fecal indicator, recent literature suggests thatrnBacteroides can potentially survive within water distribution systems.rnExperiments were performed to investigate the ability of Bacteroides to survive withinrnwater distribution systems by using a laboratory scale model water distribution system consistingrnof an independent pipe loop constructed of PVC. The model was used to investigate the survivalrnof Bacteroides in water distribution systems. The system was spiked with 10~9rnBacteroides andrnwater and biofilm samples were collected five times during the first day. The sample collectionrncontinued daily for the first week, and once a week for the subsequent six weeks. Positive culturernresults were obtained only from samples collected within the first hour after spiking. PCR assaysrnwere performed on biofilm samples collected in week seven and month four. Week sevenrnbiofilm samples were PCR positive while month four samples were PCR negative forrnBacteroides. The experiment was duplicated with analogous results.rnIn addition, field samples were collected to examine the presence of Bacteroides inrndrinking water distribution systems. Water meters were collected from water utilities withinrncentral Arizona. Upon removal for repair by city personnel, meters were immediately submergedrnin a clean bucket of water and biofilms were collected by scraping the inlet of each meter using arnbleach-sterilized nylon brush. The brush was vortexed in 20 ml of sterile buffer to recoverrnbacterial samples. The samples were then cultured using Bacteroides Bile Esculin agar in Bio-rnBagTM Anaerobic Environmental Chambers. Sixty-five samples were analyzed with no positivernculture results and 27 of the samples tested positive by PCR assay and were confirmed asrnBacteroides by DNA sequencing. Positive PCR amplicons were sequenced and compared to thernGenbank database. Sequences showed high homology (97-99%) with uncultured Bacteroides. The results of this study support the hypothesis that Bacteroides can potentially be foundrnin water distribution systems despite the difficulty of cultivating these bacterial cells. This studyrnsuggests the importance of considering biofilm interactions with fecal indicator bacteria whenrnperforming molecular assays in environmental samples. Although the significance of biofilmrninteractions with surface or recreational waters may be small, they are likely important whenrnconsidering drinking water delivered through distribution systems.