title: Irreversible UV inactivation of Cryptosporidium spp. despite the presence of UV repair genes.
abstract: Ultraviolet light is being considered as a disinfectant by the water industry because it appears to be very effective for inactivating pathogens, including Cryptosporidium parvum. However, many organisms have mechanisms for repairing ultraviolet light-induced DNA damage, which may limit the utility of this disinfection technology. Inactivation of C. parvum was assessed by measuring infectivity in cells of the human ileocecal adenocarcinoma HCT-8 cell line, with an assay targeting a heat shock protein gene and using a reverse transcriptase polymerase chain reaction to detect infections. Oocysts of five different isolates displayed similar sensitivity to ultraviolet light. An average dosage of 7.6 mJ/cm2 resulted in 99.9% inactivation, providing the first evidence that multiple isolates of C. parvum are equally sensitive to ultraviolet disinfection. Irradiated oocysts were unable to regain pre-irradiation levels of infectivity, following exposure to a broad array of potential repair conditions, such as prolonged incubation, pre-infection excystation triggers, and post-ultraviolet holding periods. A combination of data-mining and sequencing was used to identify genes for all of the major components of a nucleotide excision repair complex in C. parvum and Cryptosporidium hominis. The average similarity between the two organisms for the various genes was 96.4% (range, 92-98%). Thus, while Cryptosporidum spp. may have the potential to repair ultraviolet light-induced damage, oocyst reactivation will not occur under the standard conditions used for storage and distribution of treated drinking water.
authors.affiliation: Metropolitan Water District of Southern California, Water Quality Laboratory, La Verne, California 91750, USA. prochelle@mwdh2o.com
authors.forename: Paul A
authors.initials: PA
authors.lastname: Rochelle
authors.forename: Daffodil
authors.initials: D
authors.lastname: Fallar
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Marshall
authors.forename: Beth A
authors.initials: BA
authors.lastname: Montelone
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Upton
authors.forename: Keith
authors.initials: K
authors.lastname: Woods
mesh_terms: D000818:Animals; D002460:Cell Line; D016785:Cryptosporidium parvum / Q000235:genetics / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D004203:Disinfection / Q000379:methods; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D033661:Oocysts; D014466:Ultraviolet Rays