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Appl. Environ. Microbiol., Sep 1997, 3669-3675, Vol 63, No. 9
TR Slifko, D Friedman, JB Rose and W Jakubowski
Current assay methods to detect Cryptosporidium oocysts in water are
generally not able to evaluate viability or infectivity. A method was
developed for low-level detection of infective oocysts by using HCT-8 cells
in culture as hosts to C. parvum reproductive stages. The infective foci
were detected by labeling intracellular developmental stages of the
parasite in an indirect-antibody assay with a primary antibody specific for
reproductive stages and a secondary fluorescein isothiocyanate-conjugated
antibody. The complete assay was named the focus detection method (FDM).
The infectious foci (indicating that at least one of the four sporozoites
released from a viable oocyst had infected a cell) were enumerated by
epifluorescence microscopy and confirmed under Nomarski differential
interference contrast microscopy. Time series experiments demonstrated that
the autoreinfective life cycle in host HCT-8 cells began after 12 h of
incubation. Through dilution studies, levels as low as one infectious
oocyst were detected. The cell culture FDM compared well to other viability
assays. Vital stains and excystation demonstrated that oocyst populations
less than 1% viable (by vital dyes) and having a low sporozoite yield
following excystation could not infect host cells. Until now, the water
industry has relied on an oocyst detection method (under an information
collection regulation) that is unable to determine viability. The
quantifiable results of the cell culture method described demonstrate two
important applications: (i) an infectivity assay that may be used in
conjunction with current U.S. Environmental Protection Agency- mandated
detection methodologies, and (ii) a method to evaluate oocyst infectivity
in survival and disinfection studies.
Copyright © 1997, American Society for Microbiology
An in vitro method for detecting infectious Cryptosporidium oocysts with cell culture
Department of Marine Science, University of South Florida, St. Petersburg, USA. slifko@seas.marine.usf.edu
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