The role of biofilms in Legionella pneumophila transmission in drinking water distribution system

Legionella pneumophila;biofilms;transmission;disinfection;drinking water;biofilm stiffness;biofilm structure

Shen, Yun

关键词: Legionella pneumophila;    biofilms;    transmission;    disinfection;    drinking water;    biofilm stiffness;    biofilm structure;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/92839/SHEN-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Biofilms in drinking water distribution systems (DWDS) or premise plumbing systems could facilitate the persistence and transmission of pathogenic Legionella pneumophila (L. pneumophila), thus raise human health concerns. L. pneumophila cells can accumulate in biofilms, be protected from disinfection by biofilms, and then be released from biofilms with detached biofilm materials or by the drinking water flow shear stress. Biofilm properties (e.g., physical structure and mechanical stiffness) play an important role during this L. pneumophila transmission process. However, the knowledge on how the biofilm properties control L. pneumophila transmission and what factors in DWDS determine biofilm properties is still unclear. Therefore, this research aimed to 1) identify the key factors controlling biofilm-associated L. pneumophila accumulation, persistence, and release; 2) investigate how the biofilm structural, mechanical, and chemical properties vary in response to a complex DWDS environment.First, this research identified the effect of biofilm structure on L. pneumophila adhesion to and release from simulated drinking water biofilms. Roughness of biofilms was found to enhance the adhesion of L. pneumophila to biofilms due to enlarged biofilm surface area and local flow conditions created by roughness asperities. However, the release of L. pneumophila from biofilms was prevented by biofilms, presumably because of low shear stress zones near roughness asperities. Next, the effect of disinfectant exposure, an important parameter of drinking water quality, on biofilm structure and stiffness as well as the corresponding pathogen release and inactivation was identified. The biofilm thickness recovered during a long-term disinfectant exposure, indicating that the long-term disinfection could not significantly remove biofilms. However, the biofilms became stiffer after long-term disinfection. By using the simulated drinking water containing disinfectant to release the adhered L. pneumophila from the stiffened disinfected biofilms, the inactivation and infectivity of released L. pneumophila was examined. Compared to non-disinfected (softer) biofilms, the L. pneumophila released from disinfected (stiffer) biofilms showed higher inactivation ratio and lower infectivity. Therefore, those stiffened biofilms provided less protection for the biofilm-associated L. pneumophila under disinfectant exposure. Lastly, the role of drinking water scaling control (e.g., hardness reduction and scale inhibitor application) on the chemical composition, physical structure, and mechanical stiffness of biofilms was investigated. Applying the scale control to water source diminished the calcium carbonate precipitating inside biofilms, thus led to biofilms with low stiffness. Notably, application of scale inhibitor (polyphosphate) produced the thickest biofilms. High pathogen release would be expected from those thick and soft biofilms developed in present of polyphosphate.This research comprehensively investigated the accumulation, disinfection, and release of L. pneumophila associated with biofilms under the continuous drinking water flow and disinfectant exposure conditions, which best mimicked the DWDS in practice. The results of this study highlighted the relation between biofilms, pathogens, and drinking water, thus could provide information on risk assessment of control of pathogens in DWDS.