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Differences in staining intensities affect reported occurrences and concentrations of Giardia spp. in surface drinking water sources
Citation:
Alderiswio, K., L. Villegas, M. Ware, L. McDonald, L. Xiao, AND E. Villegas. Differences in staining intensities affect reported occurrences and concentrations of Giardia spp. in surface drinking water sources. JOURNAL OF APPLIED MICROBIOLOGY. Blackwell Publishing, Malden, MA, 123(6):1607-1613, (2017).
Impact/Purpose:
Human infectious types of Giardia and Cryptosporidium are known to cause diarrheal illness in immunocompetent individuals and can lead to additional stress and illness in the immunocompromised population (Ryan and Caccio 2013; Ryan et al. 2014; Checkley et al. 2015). To minimize risks associated with waterborne disease outbreaks caused by these pathogens, the USEPA promulgated the Long Term 2 Enhanced Surface Water Treatment Rule (LT2) (USEPA 2006) requiring drinking water utilities using surface source waters to monitor for Cryptosporidium and Giardia using USEPA Method 1623 (USEPA 2005).
Description:
Aim USEPA Method 1623, or its equivalent, is currently used to monitor for protozoan contamination of surface drinking water sources worldwide. At least three approved staining kits used for detecting Cryptosporidium and Giardia are commercially available. This study focuses on understanding the differences among staining kits used for Method 1623. Methods and Results Merifluor and EasyStain labeling kits were used to monitor Cryptosporidium oocyst and Giardia cyst densities in New York City's raw surface water sources. In the year following a change to the approved staining kits for use with Method 1623, an anomaly was noted in the occurrence of Giardia cysts in New York City's raw surface water. Specifically, Merifluor-stained samples had higher Giardia cyst densities as compared with those stained with EasyStain. Side by side comparison revealed significantly lower fluorescence intensities of Giardia muris as compared with G. duodenalis cysts when labeled with EasyStain. Conclusions This study showed very poor fluorescence intensity signals by EasyStain on G. muris cysts results in lower cyst counts, while Merifluor, with its broader Giardia cyst staining specificity, results in higher cyst counts, when using Methods 1623. Significance and Impact of Study These results suggest that detected Giardia cyst concentrations are dependent on the staining kits used, which can result in a more or less conservative estimation of occurrences and densities of zoonotic Giardia cysts by detecting a broader range of Giardia species/Assemblages.
