ARS | Publication request: Detection of castor contamination by real-time polymerase chain reaction

Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2006
Publication Date: January 24, 2007
Citation: He, X., Brandon, D.L., Chen, G.Q., McKeon, T.A., Carter, J.M. 2007. Detection of castor contamination by real-time polymerase chain reaction. Journal of Agricultural and Food Chemistry. 55(2):545-550.

Interpretive Summary: The intentional adulteration of food with ricin is a matter of increasing concern. Because crude castor seed preparations could be used as a bioweapon, we developed a screening strategy that employs sensitive detection of the DNA of the castor plant, rather than the protein toxin itself. This assay could be formatted as part of a kit to detect multiple biothreats simultaneously.

Technical Abstract: Ricin is a potent protein toxin present in the seeds of Ricinus communis (castor) plants. The intentional adulteration of food with ricin is a matter of increasing concern. We hypothesized that a PCR assay could be used to detect the castor nucleic acid that remains associated with crude toxin preparations. In this study, we developed a SYBR-Green I Dye-based real-time quantitative PCR (QPCR) method for sensitive detection of ricin DNA fragment as an indication of castor contamination in food. One primer pair was identified and confirmed to be castor-specific and efficient for amplification of ricin in DNA extracts from castor or beef matrices. Of three different DNA extraction protocols compared, the hexadecyltrimethylammonium bromide (CTAB) method yielded the highest quality of DNA for QPCR assay. The detection limit for castor contamination in ground beef samples was < 0.001% (< 10 ug of castor acetone powder per gram of beef, corresponding to 0.5 ug of ricin), indicating excellent sensitivity for the assay, and well below the threshold for oral toxicity.