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Cryptosporidium parvum inactivation experiments were performed by testing the protective effect of reactive oxygen species-degrading enzymes and scavengers on Cryptosporidium parvum oocyst viability in the presence of ultraviolet irradiation. Viability was measured by using two vital staining procedures: DAPI/PI and SYTO(R)9 staining. Enzymes/scavengers were added to the oocyst suspensions in PBS or natural water and incubated for 24 and 48 hours at 20 degrees C either in the dark or with continuous exposure to ultraviolet irradiation. The ultraviolet light intensity (365 nm) was adjusted to 3.5 mW/cm2. Thiourea (100 mM), a hydroxyl radical scavenger, exhibited the most protective effect, suggesting that hydroxyl radicals were generated by ultraviolet irradiation in both PBS and natural water and that they exerted an effect on oocyst viability. Catalase (800 U/mL), which breaks down hydrogen peroxide, also exhibited a significant protective effect on oocyst viability. Superoxide dismutase (900 U/mL), which breaks down superoxide anions to hydrogen peroxide, had no significant protective effect, suggesting that hydrogen peroxide was involved in photo-toxicity. The combination of superoxide dismutase and catalase exhibited a greater photo-protective effect in Lake Michigan samples than in PBS, indicating that the production of superoxide anions and/or hydrogen peroxide was less significant in Lake Michigan than in PBS, when subjected to ultraviolet irradiation. This study shows that certain reactive oxygen species, especially hydroxyl radicals and hydrogen peroxide, were associated with the inactivation (photo-toxicity) of Cryptosporidium parvum oocysts observed when these parasites were exposed to ultraviolet irradiation.

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Published: 01/01/1998 ISBN(s): 0898679796 Number of Pages: 8File Size: 1 file , 69 KB