Tang Mandy Lok Yi, Lau Stanley Chun Kwan
Department of Ocean Science, Hong Kong University of Science and Technology, Hong Kong, China.
Front Microbiol. 2022 Jul 11;13:919207. doi: 10.3389/fmicb.2022.919207. eCollection 2022.
Sewage effluent discharge is a major source of pathogenic contamination to the environment. The disinfection process is critical for the elimination of pathogens in sewage. In this study, we examined the impact of chlorine disinfection on the total, viable, and culturable populations of indicator bacteria, pathogens, and bacterial communities in two contrasting types of effluents (primarily treated saline and secondarily treated freshwater). Effluents collected bimonthly over 1 year were examined using cultivation, quantitative PCR (qPCR), and 16S rRNA gene amplicon sequencing coupled with or without propidium monoazide (PMA) treatment. The results showed that each type of effluent was characterized by a specific set of representative genera before disinfection. Salinity appeared to be the major abiotic factor associated with the differences in bacterial community compositions. The pathogen analysis pipeline revealed over 20 viable clinically important pathogenic species in the effluents. Although the bacterial communities differed markedly between the two types of effluents before disinfection, the species of pathogens persisting after disinfection were similar, many of them were members of and . The relative abundances of all pathogens identified in the amplicon sequences were multiplied by the 16S rRNA gene copy numbers of total bacteria detected by PMA-qPCR to estimate their concentrations. Pathogens remained viable after disinfection reached 8 log 16S rRNA copies ml effluent. Meanwhile, around 80 % of the populations of three indicator bacteria including , and Bacteroidales were viable after disinfection, but over 99 % of the viable and were in the non-culturable state. We estimated the total pathogen load by adding the concentrations of all viable pathogens and examined their correlations with indicator bacteria of different types, physiological states, and effluents. The results showed that the PMA-qPCR measurement of is a reliable proxy of bacterial pathogen loads in both types of effluents. The utility of viable indicator bacteria as a biological index to assess the overall bacteriological hazards in effluents is discussed.
污水排放是环境中致病污染物的主要来源。消毒过程对于消除污水中的病原体至关重要。在本研究中，我们考察了氯消毒对两种不同类型污水（主要是经过处理的盐水和二级处理的淡水）中指示菌、病原体以及细菌群落的总数、活菌数和可培养菌数的影响。对在1年时间里每两个月采集一次的污水样本，采用培养法、定量PCR（qPCR）以及在有或没有单叠氮化丙锭（PMA）处理的情况下进行16S rRNA基因扩增子测序来进行检测。结果表明，每种类型的污水在消毒前都具有一组特定的代表性属。盐度似乎是与细菌群落组成差异相关的主要非生物因素。病原体分析流程揭示了污水中存在20多种具有临床重要性的活菌病原体。尽管两种类型的污水在消毒前的细菌群落有显著差异，但消毒后仍存在的病原体种类相似，其中许多是 和 的成员。将扩增子序列中鉴定出的所有病原体的相对丰度乘以通过PMA-qPCR检测到的总细菌的16S rRNA基因拷贝数，以估计它们的浓度。消毒后病原体仍保持存活，达到每毫升污水8 log 16S rRNA拷贝数。与此同时，包括 、 和拟杆菌目在内的三种指示菌约80%的菌数在消毒后仍存活，但超过99%的存活 和 处于不可培养状态。我们通过将所有存活病原体的浓度相加来估计病原体总负荷，并考察了它们与不同类型、生理状态和污水的指示菌之间的相关性。结果表明，PMA-qPCR对 的测量是两种类型污水中细菌病原体负荷的可靠指标。还讨论了将活菌指示菌用作评估污水中总体细菌学危害的生物学指标的实用性。
