Effect of Particles on the Recovery of Cryptosporidium Oocysts from Source Water Samples of Various Turbidities

Abstract

Cryptosporidium parvum can be found in both source and drinking water and has been reported to cause serious waterborne outbreaks which threaten public health safety. The U.S. Environmental Protection Agency has developed method 1622 for detection of Cryptosporidium oocysts present in water. Method 1622 involves four key processing steps: filtration, immunomagnetic separation (IMS), fluorescent-antibody (FA) staining, and microscopic evaluation. The individual performance of each of these four steps was evaluated in this study. We found that the levels of recovery of C. parvum oocysts at the IMS-FA and FA staining stages were high, averaging more than 95%. In contrast, the level of recovery declined significantly, to 14.4%, when the filtration step was incorporated with tap water as a spiking medium. This observation suggested that a significant fraction of C. parvum oocysts was lost during the filtration step. When C. parvum oocysts were spiked into reclaimed water, tap water, microfiltration filtrate, and reservoir water, the highest mean level of recovery of (85.0% ؎ 5.2% [mean ؎ standard deviation]) was obtained for the relatively turbid reservoir water. Further studies indicated that it was the suspended particles present in the reservoir water that contributed to the enhanced C. parvum oocyst recovery. The levels of C. parvum oocyst recovery from spiked reservoir water with different turbidities indicated that particle size and concentration could affect oocyst recovery. Similar observations were also made when silica particles of different sizes and masses were added to seeded tap water. The optimal particle size was determined to be in the range from 5 to 40 m, and the corresponding optimal concentration of suspended particles was 1.42 g for 10 liters of tap water.

Association of Cryptosporidium parvum with Suspended Particles: Impact on Oocyst Sedimentation

“…Using direct microscopy, settling columns, and batch experiments, we demonstrated that C. parvum oocysts generally associate with suspended sediments under a wide range of background water chemistry conditions. These findings are congruent with the results of Feng et al and Medema et al (9,22), who also demonstrated through batch experiments that C. parvum oocysts associate with suspended particles. In our experiments, oocysts attached to a variety of negatively charged suspended sediments.…”

Detection and Discrimination of Cryptosporidium parvum and C. hominis in Water Samples by Immunomagnetic Separation-PCR

“…The recovery rates, however, were lower than the rates reported in other studies (1,3,17). Filtration procedures, which have been shown to result in a decrease of the recovery rate by Feng et al (3), were not performed in the present study. We evaluated the IMS sample preparation procedure by allowing the oocysts to contact suspended solids concentrated from river water.…”

Occurrences and genotypes of Cryptosporidium oocysts in river network of southern-eastern China

“…The cartridge/ foam filter and immunomagnetic separation, for their quickly filtration and specificity, were recommended for Cryptosporidium detection by the method 1623 of the USEPA, but their high cost makes it difficult to conduct environmental survey in large scale. Meanwhile, many studies have noted declines in Cryptosporidium and Giardia recovery levels to near or below minimum acceptable levels in waters of high turbidity or high total suspended solid (Krometis et al 2009;Feng et al 2003;Hu et al 2004). It is possible that Cryptosporidium oocysts, which could be adhered to particles, were still retained in the filter after elution process (Feng et al 2003).…”

“…Meanwhile, many studies have noted declines in Cryptosporidium and Giardia recovery levels to near or below minimum acceptable levels in waters of high turbidity or high total suspended solid (Krometis et al 2009;Feng et al 2003;Hu et al 2004). It is possible that Cryptosporidium oocysts, which could be adhered to particles, were still retained in the filter after elution process (Feng et al 2003). So in this study, we employed a concentration and purification method adopted by Japan including cellulose ester membrane filtration, acetone dissolution, and Percoll-sucrose flotation in succession (Japanese Ministry of Health Labor and Welfare 2007).…”