Comparison of animal infectivity and nucleic acid staining for assessment of Cryptosporidium parvum viability in water

Cryptosporidium parvum oocysts were stained with the fluorogenic dyes SYTO- 9 and SYTO-59 and sorted by flow cytometry in order to determine whether th e fluorescent staining intensity correlated with the ability of oocysts to infect neonatal CD-1 mice. Oocysts that did not fluoresce or that displayed weak fluorescent intensity when stained with SYTO-9 or SYTO-59 readily est ablished infections in mice, whereas those oocysts that fluoresced brightly did not. Although fluorescent staining profiles varied among different bat ches of oocysts, a relative cutoff in fluorescent staining intensity that c orrelated with animal infectivity was observed for all batches.