Influence of US EPA 1622 method successive steps on the viability of Cryptosporidium oocysts

Viable Cryptosporidium parvum oocysts were processed by the US EPA 1622 met hod to determine ii the procedure that requires successive filtration, elut ion and centrifugation alters their integrity and viability (determined by in vitro excystation). Oocyst seeded in tap water samples were also used to evaluate recovery efficiencies and impact of the whole procedure on oocyst viability. Filtration through Envirochek Gelman cartridge was found not to damage oocysts. The use of Laureth-12 buffer during the elution step was s hown to lead to greater spontaneous oocysts excystation than other phosphat e buffers containing between 80 and/or SDS (like the Gelman buffer). Howeve r, this drawback was widely balanced against the best efficiency of this bu ffer to elute oocysts captured by the cartridge filter and therefore agains t its high recovery efficiency. Thus, in water samples in which the oocyst concentration is expected to be low, it is more advantageous to employ the Laureth-12 buffer for the elution through it can influence viability. Centr ifugation speeds (1,000-5,000 g) did not alter oocysts.