ABSTRACTEscherichia coliis the most commonly used indicator for fecal contamination in drinking water distribution systems (WDS). The assumption is thatE. colibacteria are of enteric origin and cannot persist for long outside their host and therefore act as indicators of recent contamination events. This study investigates the fate ofE. coliin drinking water, specifically addressing survival, biofilm formation under shear stress, and regrowth in a series of laboratory-controlled experiments. We show the extended persistence of threeE. colistrains (two enteric isolates and one soil isolate) in sterile and nonsterile drinking water microcosms at 8 and 17°C, withT90(time taken for a reduction in cell number of 1 log10unit) values ranging from 17.4 ± 1.8 to 149 ± 67.7 days, using standard plate counts and a series of (reverse transcription-)quantitative PCR [(RT-)Q-PCR] assays targeting 16S rRNA,tuf,uidA, androdAgenes and transcripts. Furthermore, each strain was capable of attaching to a surface and replicating to form biofilm in the presence of nutrients under a range of shear stress values (0.6, 2.0, and 4.4 dynes [dyn] cm−2; BioFlux system; Fluxion); however, cell numbers did not increase when drinking water flowed over the biofilm (P> 0.05 byttest). Finally,E. coliregrowth within drinking water microcosms containing polyethylene PE-100 pipe wall material was not observed in the biofilm or water phase using a combination of culturing and Q-PCR methods forE. coli. The results of this work highlight that whenE. colienters drinking water it has the potential to survive and attach to surfaces but that regrowth within drinking water or biofilm is unlikely.IMPORTANCEThe provision of clean, safe drinking water is fundamental to society. WDS deliver water to consumers via a vast network of pipes. E. coliis used as an indicator organism for recent contamination events based on the premise that it cannot survive for long outside its host. A key public health concern therefore arises around the fate ofE. colion entering a WDS; its survival, ability to form a biofilm, and potential for regrowth. In particular, ifE. colibacteria have the ability to incorporate and regrow within the pipe wall biofilm of a WDS, they could reinoculate the water at a later stage. This study sheds light on the fate of environmental and enteric strains ofE. coliin drinking water showing extended survival, the potential for biofilm formation under shear stress, and importantly, that regrowth in the presence of an indigenous microbial community is unlikely.
Ecology of Nontuberculous Mycobacteria