Department of Hydraulics and Sanitation, São Carlos School of Engineering, University of São Paulo, Avenida Trabalhador São-Carlense, 400 São Carlos, São Paulo 13566-590, Brazil E-mail:
J Water Health. 2022 Aug;20(8):1188-1196. doi: 10.2166/wh.2022.092.
Giardia duodenalis is responsible for several waterborne gastrointestinal outbreaks worldwide. In addition to limitations presented by the main disinfection methods, assessing the inactivation efficiency of cysts after the treatment also poses challenges. Thus, this study aimed to use the 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) staining protocol to evaluate the viability of G. duodenalis cysts inactivated by different UV and chlorination doses and boiling times. Under epifluorescent microscopy, metabolically active cysts that presented green fluorescence were considered viable. In contrast, when no green fluorescence could be observed, organisms were considered non-viable. Although statistical analysis revealed that increasing the UV dose did not significantly decrease the percentage of viable cysts, the fluorescence signal intensity decreased considerably when the cysts were irradiated with a dose equal to or greater than 80 mJ cm. Regarding chlorination and boiling treatments, this study demonstrated that no cyst showed fluorescence at the lowest NaClO concentration (0.5 mg/L) and in the shortest boiling time (2 min). Despite some limitations regarding the use of metabolic activity as a viability marker, this methodology is rapid, easy to run and cost-effective. Thus, we conclude that the CFDA-AM staining protocol has the potential to be used to assess Giardia cyst inactivation, although further research is required.
十二指肠贾第鞭毛虫是导致全球多起水源性胃肠道疾病爆发的原因之一。除了主要消毒方法所存在的局限性外，评估处理后囊包的失活效率也具有挑战性。因此，本研究旨在使用 5-羧基荧光素二乙酸乙酰氧基甲酯（CFDA-AM）染色方案评估不同 UV 和氯化剂量以及煮沸时间灭活的十二指肠贾第鞭毛虫囊包的活力。在荧光显微镜下，呈现绿色荧光的代谢活跃的囊包被认为是有活力的。相比之下，当观察不到绿色荧光时，生物体被认为是无活力的。尽管统计分析表明，增加 UV 剂量不会显著降低有活力囊包的百分比，但当囊包被剂量等于或大于 80mJ/cm 的紫外线照射时，荧光信号强度会显著下降。关于氯化和煮沸处理，本研究表明，在最低的次氯酸钠浓度（0.5mg/L）和最短的煮沸时间（2 分钟）下，没有囊包显示荧光。尽管使用代谢活性作为活力标记存在一些局限性，但该方法快速、易于操作且具有成本效益。因此，我们得出结论，CFDA-AM 染色方案有可能用于评估贾第鞭毛虫囊包的失活，但需要进一步研究。
