Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2009
Publication Date: January 1, 2010
Citation: Macarisin, D., Bauchan, G.R., Fayer, R. 2010. Spinacia oleracea L. leaf stomata harboring Cryptosporidium parvum oocysts: A potential threat for food safety. Applied and Environmental Microbiology. 76:555-559.
Interpretive Summary: Cryptosporidiosis is typically considered a disease initiated by ingestion of drinking or recreational water contaminated with the environmentally resistant oocyst stage of the parasite passed in the feces of infected humans and animals. Oocysts have been detected in irrigation waters and these were suggested as a potential route of Cryptosporidium contamination of fresh produce. Oocysts also have been found in wash-water tanks in vegetable packinghouses. Oocysts on plant surfaces have been difficult to remove by washing and have proven resistant to disinfection. To elucidate the mechanism of C. parvum persistence on fresh produce a study was conducted on spinach plants surface-irrigated with water containing C. parvum oocysts. Using laser scanning confocal microscopy oocysts were found on the surface of leaves 2, 3, and 5 days after exposure and multiple instances of oocysts internalized within the leaf stomata, despite daily post-contamination irrigation of plants with sterile water. Because most spinach and other leafy greens are grown in areas of intensive irrigation where contamination via contact with contaminated irrigation water can be a major source of the Cryptosporidium oocysts, the present findings illustrate a potential food safety problem.
Scientific literature documents the prevalence of Cryptosporidium oocysts in irrigation waters and on fresh produce. In the present study spinach leaves were experimentally exposed to Cryptosporidium oocysts which were subsequently irrigated with clean water daily for 5 days. As determined by confocal laser microscopy, oocysts remained attached to the surface of the leaves and were observed within stomata. Once internalized, oocysts, in addition to being protected from environmental degradation, are also well shielded from brushing, sonication and other physical and chemical treatments used during postharvest processing of fresh produce, making the removal and/or neutralization of these internalized parasites almost impossible. This model demonstrates the potential difficulty in providing safe food after exposure to contaminated irrigation water.