Background - Giardia lamblia (syn. Giardia duodenalis, Giardia intestinalis) is an ubiquitous protozoan parasite causing giardiasis, a diarrheal disease, in humans and animals. In children, elderly and immunocompromised people, infection can lead to severe disease and death. Transmission and infection occurs either directly via the fecal-oral route or indirectly by ingesting contaminated water or food. Waterborne outbreaks of giardiasis are reported regularly worldwide. In Austria, giardiasis is not a reportable disease. Quantification of Giardia from water samples is expensive, complex and its occurrence is depending on infected hosts shedding cysts in the environment. C. perfringens is a generally accepted surrogate for bacterial spores as well as cysts of G. lamblia, which allows us to trace and study the fate of G. lamblia in the environment. It is part of the human intestinal flora, always shed in feces and thus a reliable human fecal indicator. Certain experiments (e.g. tracer experiments) necessitate the use of spores as a tracer. Due to its pathogenicity, it is not allowed to use C. perfringens in these experiments. Bacillus subtilis, a non-pathogenic sporeforming bacterium can be used as a surrogate for bacterial spores and Giardia cysts in these experiments. However, the methodology to quantify them in environmental water samples needs to be optimized.
Results - Most of the water samples taken at two Austrian wastewater treatment plants (WWTP) were positive for G. lamblia (91 %, 10 % and 60 %, respectively, for influent samples at WWTP1 and WWTP2, 45 % and 10 %, respectively, for effluent samples). The effect of UV irradiation on the reduction of C. perfringens spores as a waste water treatment was analysed. UV irradiation led to a mean reduction of C. perfringens spores concentrations of 1.41 log with a maximum of 2.28 log. The combination of mechanical and biological treatment followed by UV irradiation led to a mean reduction of 2.40 log with a maximum of 4.16 log. Results obtained were used to estimate the performance of the system in reducing Giardia. A series of experiments was performed to improve the current detection method for B. subtilis spores. It was shown that B. subtilis spores were very resistant against high temperatures up to 80 C and tolerated high concentrations of salt (2.5 % NaCl, 0.43 M). These findings have been used to optimize the cultivation method.
Conclusion - The study showed the importance of the use of surrogates in water quality experiments. B. subtilis could be used as a surrogate for C. perfringens spores and protozoan cysts. However, the method to isolate spores from environmental samples still has to be improved by finding ways to further decrease accompanying microbiota on nutrient-rich culture media.