Chlorine Dioxide Inactivation of Cryptosporidium parvum Oocysts and Bacterial Spore Indicators

Abstract

Cryptosporidium parvum, which is resistant to chlorine concentrations typically used in water treatment, is recognized as a significant waterborne pathogen. Recent studies have demonstrated that chlorine dioxide is a more efficient disinfectant than free chlorine against Cryptosporidium oocysts. It is not known, however, if oocysts from different suppliers are equally sensitive to chlorine dioxide. This study used both a most-probablenumber-cell culture infectivity assay and in vitro excystation to evaluate chlorine dioxide inactivation kinetics in laboratory water at pH 8 and 21°C. The two viability methods produced significantly different results (P < 0.05). Products of disinfectant concentration and contact time (Ct values) of 1,000 mg ⅐ min/liter were needed to inactivate approximately 0.5 log 10 and 2.0 log 10 units (99% inactivation) of C. parvum as measured by in vitro excystation and cell infectivity, respectively, suggesting that excystation is not an adequate viability assay. Purified oocysts originating from three different suppliers were evaluated and showed marked differences with respect to their resistance to inactivation when using chlorine dioxide. Ct values of 75, 550, and 1,000 mg ⅐ min/liter were required to achieve approximately 2.0 log 10 units of inactivation with oocysts from different sources. Finally, the study compared the relationship between easily measured indicators, including Bacillus subtilis (aerobic) spores and Clostridium sporogenes (anaerobic) spores, and C. parvum oocysts. The bacterial spores were found to be more sensitive to chlorine dioxide than C. parvum oocysts and therefore could not be used as direct indicators of C. parvum inactivation for this disinfectant. In conclusion, it is suggested that future studies address issues such as oocyst purification protocols and the genetic diversity of C. parvum, since these factors might affect oocyst disinfection sensitivity.

On the cause of the tailing phenomenon during virus disinfection by chlorine dioxide

“…Importantly, it is effective at inactivating Cryptosporidium, whereas free chlorine is not (Chauret et al, 2001). Except from exhibiting a good disinfection capacity, ClO 2 can also oxidize iron and manganese, as well as help controlling taste and odor compounds (Aieta and Berg, 1986;Li et al, 1996).…”

“…It is therefore of interest to investigate other disinfectants that have a similar disinfection potential but generate fewer problematic byproducts. As a good alternative, chlorine dioxide (ClO 2 ) has shown to efficiently disinfect water for human consumption (Huang et al, 1997;Jin et al, 2013;Zoni et al, 2007).Importantly, it is effective at inactivating Cryptosporidium, whereas free chlorine is not (Chauret et al, 2001). Except from exhibiting a good disinfection capacity, ClO 2 can also oxidize iron and manganese, as well as help controlling taste and odor compounds (Aieta and Berg, 1986;Li et al, 1996).…”

Cell Culture-Taqman PCR Assay for Evaluation of Cryptosporidium parvum Disinfection

“…Although some water treatment processes remove oocysts, any oocysts that break through represent a potential threat to human health due to their relative chlorine resistance. Various methods of disinfection have been investigated by a number of research groups; these methods include UV light (4, 10, 11, 13, 14, 23, 35), ozone (5, 18, 22, 29), chlorine dioxide (8,12,22,30,34), mixed oxidants (MIOX) (6, 40), and chlorine (7,22,17). Many disinfection studies have used animal infectivity or surrogate in vitro assays to determine the viability of oocysts after disinfection.…”

Validation of a Clostridium Endospore Viability Assay and Analysis of Greenland Ices and Atacama Desert Soils

“…Some psychrotrophic clostridia are also responsible for the spoilage of chilled vacuum-packed meat (9). In addition, C. perfringens has been used as an indicator of fecal contamination, because it is present in large numbers in human and animal wastes (4,6). Due to their resistance to various extreme conditions, Clostridium endospores are also employed as biological indicators to monitor the effectiveness of various sterilization processes (11,12).…”