Environmental temperature controls Cryptosporidium oocyst metabolic rate and associated retention of infectivity.
Cryptosporidium is a significant cause of water-borne enteric disease throughout the world and represents a challenge to the water industry and a threat to public health. In this study we report the use of a cell culture-TaqMan PCR assay to measure oocyst inactivation rates in reagent-grade and environmental waters over a range of temperatures. While oocysts incubated at 4 degrees C and 15 degrees C remained infective over the 12-week holding period, we observed a 4 log(10) reduction in infectivity for both 20 and 25 degrees C incubation treatments at 12 and 8 weeks, respectively, for all water types examined, a faster rate of inactivation for oocysts than previously reported. This temperature-dependent inactivation was further investigated using a simple and rapid ATP assay described herein. Time course experiments performed in reagent-grade water at incubation temperatures of 4, 15, 20, 25, 30, and 37 degrees C identified a close relationship between oocyst infectivity and oocyst ATP content, demonstrating that temperature inactivation at higher temperatures is a function of increased oocyst metabolic activity. While water quality did not affect oocyst inactivation, biological antagonism appears to be a key factor affecting oocyst removal from environmental waters. Both the cell culture-TaqMan PCR assay and the ATP assay provide a sensitive and quantitative method for the determination of environmental oocyst inactivation, providing an alternative to the more costly and time-consuming mouse infection assay. The findings presented here relating temperature to oocyst inactivation provide valuable information for determining the relative risks associated with Cryptosporidium oocysts in water.
Co-operative Research Centre for Water Quality and Treatment, Australian Water Quality Centre, SA Water Corporation, Salisbury, South Australia 5108, Australia.
Brendon J
BJ
King
Alexandra R
AR
Keegan
Paul T
PT
Monis
Christopher P
CP
Saint
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D016785:Cryptosporidium parvum / Q000254:growth & development* / Q000378:metabolism / Q000472:pathogenicity; D005618:Fresh Water / Q000469:parasitology*; D051379:Mice; D033661:Oocysts / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity*; D016133:Polymerase Chain Reaction; D019914:Taq Polymerase / Q000378:metabolism; D013696:Temperature
D000255:Adenosine Triphosphate; D019914:Taq Polymerase