School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
Int J Hyg Environ Health. 2019 May;222(4):678-686. doi: 10.1016/j.ijheh.2019.04.007. Epub 2019 Apr 27.
Prolific growth of pathogenic Legionella pneumophila within engineered water systems and premise plumbing, and human exposure to aerosols containing this bacterium results in the leading health burden of any water-related pathogen in developed regions. Ecologically, free-living amoebae (FLA) are an important group of the microbial community that influence biofilm bacterial diversity in the piped-water environment. Using fluorescent microscopy, we studied in-situ the colonization of L. pneumophila in the presence of two water-related FLA species, Willaertia magna and Acanthamoeba polyphaga in drinking water biofilms. During water flow as well as after periods of long-stagnation, the attachment and colonization of L. pneumophila to predeveloped water-biofilm was limited. Furthermore, W. magna and A. polyphaga showed no immediate interactions with L. pneumophila when introduced to the same natural biofilm environment. A. polyphaga encysted within 5-7 d after introduction to the tap-water biofilms and mostly persisted in cysts till the end of the study period (850 d). W. magna trophozoites, however, exhibited a time delay in feeding on Legionella and were observed with internalized L. pneumophila cells after 3 weeks from their introduction to the end of the study period and supported putative (yet limited) intracellular growth. The culturable L.pneumophila in the bulk water was reduced by 2-log over 2 years at room temperature but increased (without a change in mip gene copies by qPCR) when the temperature was elevated to 40 °C within the same closed-loop tap-water system without the addition of nutrients or fresh water. The overall results suggest that L. pneumophila maintains an ecological balance with FLA within the biofilm environment, and higher temperature improve the viability of L. pneumophila cells, and intracellular growth of Legionella is possibly cell-concentration dependent. Observing the preferential feeding behavior, we hypothesize that an initial increase of FLA numbers through feeding on a range of other available bacteria could lead to an enrichment of L. pneumophila, and later force predation of Legionella by the amoeba trophozoites results in rapid intracellular replication, leading to problematic concentration of L. pneumophila in water. In order to find sustainable control options for legionellae and various other saprozoic, amoeba-resisting bacterial pathogens, this work emphasizes the need for better understanding of the FLA feeding behavior and the range of ecological interactions impacting microbial population dynamics within engineered water systems.
在工程化的水系统和建筑物管道中，致病性嗜肺军团菌大量繁殖，人类吸入含有这种细菌的气溶胶，导致在发达地区，军团菌成为与水相关的病原体中对健康造成最大负担的病原体。从生态学角度看，自由生活阿米巴原虫（FLA）是微生物群落中的一个重要群体，它影响着管道水环境中生物膜细菌的多样性。我们使用荧光显微镜研究了在饮用水生物膜中存在两种与水有关的 FLA 物种（巨大威氏阿米巴和多形普氏阿米巴）时，嗜肺军团菌的原位定植情况。在水流以及长时间停滞期间，军团菌对预先形成的水生物膜的附着和定植受到限制。此外，当将巨大威氏阿米巴和多形普氏阿米巴引入相同的天然生物膜环境时，它们与嗜肺军团菌没有立即相互作用。多形普氏阿米巴在引入自来水生物膜后 5-7 天内形成包囊，并且在研究结束时（850 天）主要以包囊形式存在。然而，巨大威氏阿米巴滋养体在吞噬军团菌时表现出时间延迟，并且在从引入到研究结束的 3 周后，观察到内部含有嗜肺军团菌细胞，并支持潜在的（但有限的）细胞内生长。在没有添加营养物质或淡水的情况下，将同一封闭回路自来水系统中的温度升高到 40°C 时，可在 2 年内使可培养的嗜肺军团菌在总水中减少 2 个对数，但军团菌 mip 基因的拷贝数（qPCR）不变。总体结果表明，嗜肺军团菌与生物膜环境中的 FLA 保持生态平衡，较高的温度可提高军团菌细胞的活力，并且军团菌的细胞内生长可能与细胞浓度有关。观察到优先的取食行为后，我们假设通过取食一系列其他可用细菌，FLA 数量的最初增加可能导致嗜肺军团菌的富集，随后，阿米巴滋养体对军团菌的捕食导致快速的细胞内复制，从而导致水中嗜肺军团菌浓度出现问题。为了找到针对军团菌和各种其他需氧阿米巴抵抗性细菌病原体的可持续控制选择，这项工作强调需要更好地了解 FLA 的取食行为以及影响工程化水系统中微生物种群动态的生态相互作用范围。
