Low-pressure UV inactivation and DNA repair potential of Cryptosporidium parvum oocysts

Because Cryptosporidium parvum oocysts are very resistant to conventional w ater treatment processes, including chemical disinfection, we determined th e kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp W radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose sus pensions of purified C, parvum oocysts in phosphate-buffered saline, pH 7.3 , at 25 degreesC to various doses of monochromatic LP W, C, parvum infectiv ity reductions were rapid, approximately first order, and at a dose of 3 mJ /cm(2) (=30 J/m(2)), the reduction reached the cell culture assay detection limit of similar to3 log(10). At UV doses of 1.2 and 3 mJ/cm(2), the log(1 0) reductions of C, parvum oocyst infectivity were not significantly differ ent for control oocysts and those exposed to dark or light repair condition s for UV-induced DNA damage. These results indicate that C, parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radi ation and that there is no phenotypic evidence of either light or dark repa ir of UV-induced DNA damage.