Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2009
Publication Date: 10/15/2009
Citation: Rasooly, R., Do, P.M. 2009. Shiga toxin Stx2 is heat-stable and not inactivated by pasteurization. International Journal of Food Microbiology. 136(2010):290-294
Interpretive Summary: Shiga toxins produced mostly by Shigella dysenteriae and Escherichia coli 0157:H7 cause approximately 73,000 cases illness per year and 61 deaths annually in the United States. Consumption of unpasteurized raw milk has resulted in illnesses ranging from mild intestinal disease to severe kidney complications. Most milk consumed in the United States is pasteurized, which eliminates almost all pathogens. However, there are no studies that show whether pasteurization inactivates shiga toxins, and this remains an open question. Our data demonstrate that shiga toxin is heat-stable, and that pasteurization of milk at the temperatures and times approved by the U.S. Food and Drug Administration does not inactivate the toxin. These data suggest that shiga toxin is not inactivated by regular pasteurization.
Technical Abstract: Shiga toxins are expressed by Escherichia coli (STEC) and are associated with food-borne diseases. Pasteurization is used to retard microbial growth in milk, and an open question is whether milk pasteurization inactivates shiga toxins. To answer this question we measure shiga toxin’s inhibition effect on Vero cells dehydrogenase activity and protein synthesis. Our data demonstrate that shiga toxin 2 (Stx2) is heat-stable and that pasteurization of milk, at the various suggested temperatures and times by the U.S. Food and Drug Administration, at 63°C for 30 minutes, or 72°C for 15 seconds or 89°C for 1 second, did not reduce the biological activity of stx2. However, treatment at 99°C for 5 minutes inactivated the toxin. These data demonstrate that stx2 is not inactivated by regular pasteurization.