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Recent studies have shown that Cryptosporidium is very susceptible to ultraviolet (UV) light disinfection, with doses as low as = 25 mJ cm-2 resulting in approximately 3 log10 reduction in infectivity. Mouse or in vitro cell culture infectivity models have most frequently been used to measure oocyst inactivation. However, these methods are costly, labor-intensive, and require several days to weeks to perform. These methods are also impractical for the routine evaluation of typical full-scale application UV doses in the 40 to 60 mJ cm-2 range. Prior to this work, there have been no methods developed for the direct quantitation of UV-induced damage to Cryptosporidium oocysts. In this study, a bench-scale monochromatic 254 nm low-pressure UV system was used to deliver 0 to 1000 mJ cm-2 doses to C. parvum oocysts suspended in reagent water. Quantitative sequence detection (QSD), a real-time quantitative polymerase chain reaction (PCR) method, was used to directly quantify UV-induced damage in low numbers (~200) of oocysts. QSD allows the comparison of nucleic acid samples based on their amplification kinetics (i.e. "amplifiability"), and it was hypothesized that UV-induced damage to oocysts would quantitatively affect DNA amplification. QSD amplification at 10, 20, 40, 60 and 100 mJ cm-2 doses could readily be distinguished from each other (P = 0.01). Average standard deviation of all replicates for all UV doses was 16.1%. DNA of oocysts exposed to 1000 mJ cm-2 was not amplifiable. The developed method could be useful in assessing UV reactor performance and for evaluating the DNA repair potential of Cryptosporidium. Includes 8 references, figures.

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Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 5 File Size: 1 file , 260 KB