Cryptosporidium parvum and Giardia lamblia are common waterborne agents whose potential for transmission via foods is increasingly being recognized. The objectives of this study are to develop quantitative viability assays for C. parvum and G. lamblia based on cell culture or in vitro culture and ELISA, and to evaluate the methods in trials of killing the protozoan oocysts or cysts by various means pertinent to food safety.
Oocysts or cysts, respectively, will be inoculated into foods at risk of protozoan contamination (e.g., apple juice, shellfish, etc.); foods will be suspended in diluent as necessary, and the oocysts or cysts will be recovered by immunomagnetic capture. The oocysts or cysts will be treated to induce excystation, diluted serially, and inoculated into ELISA plate wells. Amplification of viable infectious agents will take place in the plate wells, during approximately 24 h at 37+ C. Oocysts of C. parvum will be amplified in plate wells that contain monolayers of BSC-1 cells; whereas G. lamblia cysts will probably be amplified in artificial medium in the wells. Homologous antibody will be added and labeled indirectly with horseradish peroxidase. The wells will be washed, a color reaction carried out, and results determined in a standard ELISA plate reader. Control inocula will include oocysts or cysts that have been inactivated by ultraviolet, formaldehyde, freezing, or heat. The tests will then be applied in inactivation trials with viable oocysts or cysts in foods of interest or in water that might be used in food processing.