Towards standard methods for the detection of Cryptosporidium parvum on lettuce and raspberries. Part 2: Validation

A reduced-cost approach for analyzing fresh produce for contamination with Cryptosporidium oocysts and/or Giardia cysts

“…Given the low level of parasites tested in this case it seems possible that this was natural contamination rather than cross-contamination in the laboratory. In the exercise by Cook et al (2006b), five out of eight labs detected Cryptosporidium oocysts on samples that were known to be negative, and thus these results compare favorably.…”

“…fresh produce with only Cryptosporidium oocysts (Cook et al, 2006b), the already spiked samples were distributed to the expert labs (8 labs, all in UK). Three levels of spike were used and also negative controls.…”

“…ISO 15553, 2006;US EPA 1623, 2005. Initial work in developing a Standard Method for analyzing fresh produce for contamination has largely focused upon these two parasites, and the methods have been based broadly on the water method, with elution from the surfaces of the fresh produce as the initial steps (Cook et al, 2006a(Cook et al, , 2006b(Cook et al, , 2007Robertson & Gjerde, 2000. In brief, these methods depend on an elution step, followed by concentration based on centrifugation and immunomagnetic separation (IMS), and detection by immunofluorescent antibody testing (IFAT).…”

“…In brief, these methods depend on an elution step, followed by concentration based on centrifugation and immunomagnetic separation (IMS), and detection by immunofluorescent antibody testing (IFAT). The method described by Cook et al (2006a), has been tested in a round-robin interlaboratory trial (Cook et al, 2006b). This method has been used as the basis for the development of an ISO Standard Method (ISO 18744; Microbiology of the food chain -Detection and enumeration of Cryptosporidium and Giardia in fresh leafy green vegetables and berry fruits), which is in the final stages of adjustment and approval before release.…”

“…In this case, the concerns include that the recovery efficiencies achieved by Cook et al (2006aCook et al ( , 2007 were not duplicated in independent or semiindependent studies (e.g. Amoros, Alonso, & Cuesta, 2010;Rzezutka et al, 2010); even in the validation studies in which 'expert' labs participated, although recovery efficiencies for Cryptosporidium from raspberries were similar to those of the developing lab, the recovery efficiencies of Cryptosporidium from lettuce were significantly lower (Cook et al, 2006b) and also misidentification of oocysts was a problem, despite the participating labs being described as 'expert'. Furthermore, the Standard ISO Method 18744 is for both Cryptosporidium and Giardia, but the publications on which the Standard Method are largely based (Cook et al, 2006a(Cook et al, , 2006b, only address Cryptosporidium parvum.…”