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1 September 2004 Irreversible UV Inactivation of Cryptosporidium spp. Despite the Presence of UV Repair Genes
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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.

PAUL A. ROCHELLE, DAFFODIL FALLAR, MARILYN M. MARSHALL, BETH A. MONTELONE, STEVE J. UPTON, and KEITH WOODS "Irreversible UV Inactivation of Cryptosporidium spp. Despite the Presence of UV Repair Genes," The Journal of Eukaryotic Microbiology 51(5), 553-562, (1 September 2004).
Received: 6 October 2003; Accepted: 1 June 2004; Published: 1 September 2004

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