Template preparation for PCR and RFLP of amplification products for the detection and identification of Cyclospora sp. and Eimeria spp. Oocysts directly from raspberries.

Raspberries were epidemiologically associated with cyclosporiasis outbreaks during 1996 and 1997. The 18S rRNA genes of Cyclospora cayetanensis and several species of a closely related genus, Eimeria, were sequenced and primers for a nested PCR developed in a previous study. The ability to distinguish amplified products of Cyclospora sp. from those of Eimeria spp. is important for testing food and environmental samples. Therefore, an RFLP analysis of amplified products was used to differentiate Cyclospora cayetanensis from Eimeria spp. PCR inhibitors and the low levels of Cyclospora oocysts present in raspberries make template preparation for PCR challenging. Several approaches for PCR template preparation from raspberry samples were evaluated. Template preparation methods using various washing and concentration steps, oocyst disruption protocols, resin matrix treatment, DNA precipitation, and/or the addition of nonfat dried milk solution to a PCR using modified primers were evaluated first with oocysts of Eimeria tenella then refined with oocysts of C. cayetanensis. Approximately 10 E. tenella oocysts per PCR or approximately 19 C. cayetanensis oocysts per PCR were detected with the optimized template preparation method. The addition of 20 microliters of raspberry wash sediment extract and nonfat dried milk solution did not inhibit the amplification of DNA from as few as 10 E. tenella and 25 C. cayetanensis oocysts in a 100-microliter PCR. The nucleotide sequences of C. cayetanensis and the Eimeria spp. are 94 to 96% similar in the amplified region, but the amplification products from the two genera were distinguished using an RFLP analysis with the restriction enzyme MnlI.