Rejoining of gamma-ray-induced DNA damage in Cryptosporidium parvum measured by the comet assay.
Cryptosporidium parvum is a well-known waterborne intracellular protozoan that causes severe diarrheal illness in immunocompromised individuals. This organism is highly resistant to harsh environmental conditions and various disinfectants, and it exhibits one of the highest known resistances to gamma irradiation. We investigated rejoining of gamma-ray-induced DNA damage in C. parvum by neutral comet assay. Oocysts were gamma irradiated at various doses (1, 5, 10, and 25kGy) and were incubated for various periods (6-96h) after exposure to 10kGy. The comet tail moment showed that the number of DNA double-strand breaks increased concomitantly with the gamma irradiation dose. When investigating rejoining after irradiation at 10kGy, double-strand breaks peaked at 6h postirradiation, and rejoining was highest at 72h postirradiation. The observed rejoining pattern suggests that repair process occurs slowly even when complex DNA double-strand breaks in C. parvum were induced by high dose irradiation, 10kGy.