Emerging protozoan parasites and food safety: investigation in 'ready to eat' packaged salads by microscopy and molecular tools

Abstract

To investigate the prevalence of protozoan contamination by Giardia duodenalis, Cryptosporidium spp., Toxoplasma gondii and Cyclospora cayetanensis, in ‘ready to eat’ (RTE) salads on sale in Italy, 648 packages from industrial and local brands were purchased. Nine individual packages from each brand were collected per month, pooled and subjected to microscopy and molecular analyses. 864 slides were microscopically examined and Cryptosporidium spp. and also Blastocystis hominis and Dientamoeba fragilis were detected. By molecular tools G. duodenalis assemblage A, Cryptosporidium parvum and Cryptosporidium ubiquitum, T. gondii Type I and C. cayetanensis were identified. B. hominis and D. fragilis were also molecularly confirmed. The overall prevalence of each protozoan species was 0.6% for G. duodenalis, 0.8% for T. gondii, 0.9% for Cryptosporidium spp., and 1.3% for C. cayetanensis, whereas the prevalence of B. hominis and D. fragilis were 0.5% and 0.2%, respectively. By microscopy and/or molecular tools, 4.2% of the samples were contaminated by at least one protozoan species, and 0.6% of them showed contamination of two protozoan species with a range number of oocysts from 62 to 554 per g of vegetable for T. gondii, and 46 to 1.580 for C. cayetanensis. This is the Europe’s first large-scale study on the presence of protozoans in packaged salads. The results show that the prevalence of protozoan species in RTE salads is a cause for concern about human health in Europe, and in particular in Italy. Pending the inclusion of protozoan parasites in EU and Italian legislation to reduce the risks of RTE contamination and minimize their foodborne transmission, our results indicate the need for additional surveillance studies of possible sources of food contamination. The sampling methods designed in this research and the results obtained can provide the direction for monitoring fresh produce in other areas, and for surveillance studies on products. In addition, they can provide the basis for food safety guidelines, based also on the HACCP system, in order to reduce the risk of RTE contamination and to minimize foodborne disease transmission