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Cookie Dough – Gooey, Sweet, and Seasoned with… Bacteria?!

Categories: Foodborne

3 magnetic beads about 5 microns in diameter.

The possibility that E. coli O157:H7 was a contaminant in cookie dough surprised even the most experienced microbiologists here in CDC’s Enteric Diseases Laboratory Branch. E. coli O157 is a common culprit of a severe diarrheal illness, usually caused by eating contaminated and undercooked ground beef or drinking unpasteurized apple juice. It shouldn’t have even been on the “Who’s Who” list of the top bacterial contaminants.

We are Gerry Gómez and Mike Humphrys, two microbiologists in the Enteric Diseases Laboratory Branch. We identify disease-causing bacteria from foods and from specimens taken from sick people.

As microbiologists we have to be flexible and creative in our approaches to isolate bacteria from all different kinds of foods. Our usual method is to mix the food with enrichment broth and see what grows after 18 hours of incubation. For this investigation, we made cookie dough slurry. Then we added tiny magnetic beads treated so they’ll stick to the antigen on the cell wall of E. coli bacteria. If present, E. coli cells would stick to the beads, and then we used a magnet to pull the beads (and any bacteria) out of the slurry. Now we had a better chance of isolating E. coli from the cookie dough.

An important part of our investigational process is collecting and sharing data from laboratories across the U.S. For the cookie dough outbreak, 13 laboratories tested 164 various cookie dough products.

E. coli growing on blood agar.

E. coli growing on blood agar.

We found that the chocolate chip cookie dough that sick people had eaten didn’t come from only one batch.

We in EDLB never know what food products will come our way, but we’re willing to test just about anything to confirm a hypothesis. Even experienced microbiologists who have “seen it all” can be surprised and challenged by an old bacteria turning up in a new place.

Public Comments

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this blog is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

  1. October 3, 2009 at 9:40 am ET  -   Dawn

    I will remember this the next time I buy a pre-mix of cookie dough. Thanks for the info.

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  2. October 3, 2009 at 8:15 pm ET  -   David Schroeder

    Doesn’t the heat during the baking process of baking cookies kill the eColi?

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  3. AUTHOR COMMENT October 15, 2009 at 2:39 pm ET  -   Gerry Gómez

    Yes David, cooking the cookie dough as directed on the package should kill any E. coli bacteria in the product. Specific to the recently recalled cookie dough, cooking the dough was not recommended because there was concern of cross-contamination.( However, in general, consumers should not eat raw food products that are intended for cooking or baking before consumption, such as cookie dough. Consumers should use safe food-handling practices when preparing such products, including following package directions for cooking at proper temperatures; washing hands, surfaces, and utensils after contact with these types of products; avoiding cross contamination; and refrigerating products properly. More information about e. coli may be found at

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  4. March 18, 2010 at 11:47 am ET  -   crystals

    Well said, “…but we’re willing to test just about anything to confirm a hypothesis.”

    When i want to test certain hypothesis on crystals energy, I have the same mindset.

    Thanks for being professional and responsible. We know we can count on you.

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  5. March 5, 2011 at 1:27 am ET  -   Hridoy

    This site is really resourceful.

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  6. June 5, 2011 at 11:01 pm ET  -   used ipad for sale

    By and large I don’t post comments on websites, but I’d like to mention that this post really has forced me to do so! Thank you for your perceptive post.

    Link to this comment

  7. October 30, 2012 at 7:27 pm ET  -   Ken Johnson

    My children love raw cookie dough. I now know it is not safe. Thank you.

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