Affiliation:
1. Biological and Physical Sciences Unit, Indiana University Kokomo, Kokomo, Indiana 46904-9003,1 and
2. Department of Civil Engineering, University of Toronto, Toronto, Ontario, Canada M5S 1A42
Abstract
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-probable-number–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 · 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 · 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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Reference33 articles.
1. American Public Health Association
(1998) Standard methods for the examination of water and wastewater (American Public Health Association Washington D.C.) 20th ed.
2. Atlas
R.
(1997) Handbook of microbiological media. (CRC Press Inc.Boca Raton Fla).
3. Nucleic acid stains as indicators of Cryptosporidium parvum oocyst viability;Belosevic M.;Int. J. Parasitol.,1997
4. Medium-pressure UV for oocyst inactivation;Bukhari Z.;J. Am. Water Works Assoc.,1998
5. Chlorine disinfection of recreational water for Cryptosporidium parvum;Carpenter C.;Emerg. Infect. Dis.,1999
Cited by
98 articles.
订阅此论文施引文献
订阅此论文施引文献，注册后可以免费订阅5篇论文的施引文献，订阅后可以查看论文全部施引文献