Kibbee Richard J, Örmeci Banu
Department of Civil and Environmental Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada.
Department of Civil and Environmental Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada.
J Microbiol Methods. 2017 Jan;132:139-147. doi: 10.1016/j.mimet.2016.12.004. Epub 2016 Dec 6.
The detection and quantification of viable Escherichia coli cells in wastewater treatment plant effluent is very important as it is the main disinfection efficacy parameter for assessing its public health risk and environmental impact. The aim of this study was to develop a sensitive and false-positive free propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) assay to quantify the viable but non-culturable (VBNC) E. coli present in secondary wastewater effluent after chlorine disinfection. The qPCR target was the E. coli uidA gene, and native Taq was used to eliminate false positives caused by the presence of contaminant E. coli DNA in recombinant Taq polymerase reagents. Due to issues with qPCR inhibitors in wastewater, this study explored several pre-DNA extraction treatment methods for qPCR inhibitor removal. PMA-qPCR validation was done using salmon testes DNA (Sketa DNA) as an exogenous control added directly to the wastewater samples and amplified using a separate qPCR assay. After disinfection of secondary effluent with 2ppm chlorine at the plant, the mean Log CFU reduction in E. coli was 2.85 from a mean CFU of 3.48/10mL compared to 0.21 Log CCE mean reduction of the uidA gene from a mean CCE of 3.16/10mL. The VBNC cell concentrations were calculated as 2.32 Log/10mL by subtracting the colony forming units (CFU) obtained from membrane filtration from the calculated CFU equivalent (CCE) values obtained from PMA-qPCR. These results demonstrate the effective use of a PMA-qPCR method for the quantification of the E. coli uidA gene and indicate there are high numbers (2.01×10CCE/100mL) of VBNC E. coli cells leaving the wastewater treatment plant in the final effluent after chlorine treatment. VBNC bacterial cells are of concern as they have the potential to resuscitate and grow, regain virulence, affect natural microbiome in the discharge sites, and pass on antimicrobial resistant genes to other microorganisms.
检测和量化污水处理厂废水中活的大肠杆菌细胞非常重要,因为它是评估其公共卫生风险和环境影响的主要消毒效果参数。本研究的目的是开发一种灵敏且无假阳性的单叠氮碘化丙啶-定量聚合酶链反应(PMA-qPCR)检测方法,以量化氯消毒后二级废水排放物中存在的活的但不可培养(VBNC)的大肠杆菌。qPCR的靶标是大肠杆菌的uidA基因,使用天然Taq酶来消除重组Taq聚合酶试剂中污染的大肠杆菌DNA导致的假阳性。由于废水中存在qPCR抑制剂问题,本研究探索了几种用于去除qPCR抑制剂的DNA提取前处理方法。使用鲑鱼精巢DNA(Sketa DNA)作为外源对照直接添加到废水样品中,并通过单独的qPCR检测进行扩增,以此对PMA-qPCR进行验证。在工厂用2ppm氯对二级出水进行消毒后,大肠杆菌的平均Log CFU减少量为2.85,初始平均CFU为3.48/10mL,相比之下,uidA基因的平均CCE减少量为0.21 Log,初始平均CCE为3.16/10mL。通过从PMA-qPCR获得的计算出的CFU当量(CCE)值中减去膜过滤获得的菌落形成单位(CFU),计算出VBNC细胞浓度为2.32 Log/10mL。这些结果证明了PMA-qPCR方法在量化大肠杆菌uidA基因方面的有效应用,并表明在氯处理后的最终排放物中,有大量(2.01×10CCE/100mL)的VBNC大肠杆菌细胞离开污水处理厂。VBNC细菌细胞令人担忧,因为它们有可能复苏并生长、恢复毒力、影响排放地点的自然微生物群落,并将抗微生物耐药基因传递给其他微生物。