Why flour can harbour dangerous E. coli bacteria

There are good reasons why food safety experts say "do not eat raw dough or batter." Bacteria from grain elevators or flour mills can travel to your kitchen.

Contamination from food processing plants can travel to the kitchen

Flour or other ingredients used to make raw dough or batter might be contaminated with bacteria that can make you seriously sick. (Matthew Mead/Associated Press)

As tempting as it may be to sample freshly beaten cake mix or cookie dough, your stomach could regret it, depending on where the ingredients came from and how they were produced.

This week's Betty Crocker cake mix recall in Canada because of flour that may be contaminated with a nasty strain of E. coli is a reminder to cook ingredients thoroughly, including powders like flour, public health authorities say.

"Do not eat raw dough or batter, whether made from recalled flour or any other flour. Flour or other ingredients used to make raw dough or batter might be contaminated," the U.S. Centers for Disease Control and Prevention advises.

Rick Holley, a professor emeritus of food safety at the University of Manitoba in Winnipeg, is working to understand the root causes of how bacteria that grow harmlessly in ruminant livestock can end up sickening and even killing people.

Uncooked food not sterile

Holley likens eating foods that aren't well cooked to the risks people take when they jaywalk and don't cross the street at a traffic light or stop sign.

"We know only too well that there are folks who like to eat food that's not well cooked or isn't cooked and against the best advice, because the food we eat is not sterile — there are risks associated with it. Having said that, I enjoy my salad in the summer time. Uncooked."

A couple of steps back from the kitchen, bacteria like the E. coli O121 implicated in flour samples from a General Mill's facility in Kansas have been found to grow in grain elevators and equipment used to mill flour when humidity conditions are favourable.

"Where we need also to do some work is on maintaining and improving the levels of sanitation in all parts of the food system, food processing plants. We know from investigations that have been done both in Canada and the United States that when there are lapses in sanitation, problems occur in food processing plants. We can see it now happening in mills."

Most E. coli are harmless. But the E. coli that cause "hamburger disease," E. coli O157:H7, is the most notorious and deadliest of the microbes that produce a "shiga-toxin." In humans, the potent toxin can lead to a fatal condition called hemolytic uremic syndrome. The severe disease occurs in about 10 per cent of those with bloody diarrhea from the pathogen. 

E. coli O121, which is implicated in the flour recall, hasn't turned deadly. It is making some people seriously ill in the U.S.

Federal, provincial and U.S. governments are funding research to learn more about how to reduce these dangerous E. coli strains on fresh produce, such as the 2011 outbreak in Germany and France traced to fenugreek sprouts that severely sickened nearly 4,000.

With files from CBC's Amina Zafar


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