Adhesive-tape recovery combined with molecular and microscopic testing for the detection of Cryptosporidium oocysts on experimentally contaminated fresh produce and a food preparation surface

Abstract

A proof of concept study was conducted to determine if transparent double-sided adhesive tape could be used to recover and detect [by polymerase chain reaction (PCR) and immunofluorescence microscopy (IFA)] Cryptosporidium parvum oocysts on fresh produce and on a food preparation surface. Oocysts were applied on the surface of ten apples, ten peaches, eight cucumbers, and eight tomatoes within circles drawn with a permanent marker. Approximately 18h later, skin excised from three uncontaminated and three contaminated circles from each piece of produce was subjected to PCR. Pieces of transparent double-sided adhesive tape were lightly pressed onto the surface of three other contaminated circles and examined by PCR. Other pieces of adhesive tape were pressed against the surfaces of three other circles and examined by IFA. At concentrations of 100 and 50 oocysts per circle, every produce item examined by PCR of contaminated excised skin was found positive, and every item examined by adhesive tape subjected to PCR and IFA was found positive, except one. At ten oocysts per circle, every produce item was found positive by PCR of contaminated excised skin, and all apples, cucumbers, and tomatoes were found positive by adhesive tape subjected to IFA. Detection of low numbers of oocysts on peaches by IFA examination of adhesive tape was problematic because trichomes that cover peaches and impart the fuzzy surface partially restrict the tape from reaching some areas where oocysts adhere. Tape combined with IFA was successful in recovering and identifying oocysts from six areas of laminate countertop where the oocysts had been applied and allowed to dry for 30-60min. These are the first findings to demonstrate that adhesive tape can be used to recover and identify a protozoan parasite from fresh produce and from a laminate food preparation surface.