Keeping E. coli O121 Out of Flour

FQU0416_BakingAs kids, we used to help our mom clean the kitchen while the cookies were baking in the oven. We would diligently wipe the beaters and bowls clean of cookie dough and fight over any chocolate chips. Those days are sadly gone. The FDA recently sent warnings that raw cookie dough must not be consumed. Not due to the raw eggs in the dough, but gasp, cough, the flour! Yes, a 30 million pound recall of flour has expanded in scope several times due to the presence of E. coli O121.

E. coli non–O157 STEC Background

Most members of Escherichia coli (E. coli) are harmless and live in a symbiotic relationship in the intestinal tracts of humans and animals. However, a few strains are pathogenic and can cause serious disease. Certain E. coli, called Shiga-toxin E. coli (STEC), cause disease through the production of a “Shiga” toxin that is excreted in the intestine once the organism is ingested. E. coli O157:H7 is the most notorious of this group. One egregious property of the STEC group is the low infectious dose. It has been reported that doses as low as 10-100 colony-forming units can lead to symptoms, which include bloody diarrhea and can lead to kidney failure, especially in the very young, elderly, or immunocompromised individuals. Beyond E. coli O157, approximately 70 percent of non-O157 STEC infections in the U.S. are caused by six other species and have been coined the Big 6: O26, O45, O103, O 111, O121, and O145. Of those, approximately 6 percent of the overall infections were caused by O121.

Cattle have been identified as the major source for O157 and non-O157 STEC. Thus bovine intestinal matter cross-contaminating onto raw meat is the predominant vehicle of transmission. Nevertheless, non-meat foods have also been implicated in outbreaks and include milk, produce, and water. Now, flour can be added to the list. It seems doubtful that these food groups are sources in and of themselves, rather they have been cross-contaminated likely from a bovine source. For instance, contaminated irrigation water may be a source for agricultural products. Person-to-person transmission has also been identified as a potential route of exposure.

In regards to testing, most STEC testing methods are validated for use with meat and poultry products, but unfortunately not other food matrices. The current STEC testing methods involve an initial rapid screening that will identify if one of the Big 6 non-O157 STEC is present. Testing may be stopped at this point and corrective/preventative actions taken. If testing continues, the screening data will be confirmed through a series of complex assays. Technically trained scientists are needed to carry out the confirmation methods due to their complexity. The results, depending on the test method, will not distinguish between the species but merely confirm that a non-0157 STEC is present in the sample.

The recent flour recall may prompt test methodology to expand from its current focus of meat-based products to other food matrices. For those non-meat or poultry-based producers, if testing for non-O157 STEC is conducted, testing options should be discussed. It is also important that the test be validated for the test matrix. Validating the test method with the matrices is a critical component for data integrity. Furthermore, due to the confirmation complexity, the producer may want to verify that the lab be certified to perform these test methods. One certification tool is ISO 17025 and most labs will publish the test methods pertaining to their certification.

In-Plant Procedures for Keeping Non-O157 E. coli Out of Finished Product

Millers. When lots can be segregated because of daily validated wet cleaning and sanitation procedures, the “clean-up to clean-up timeframe” effectually breaks a production cycle. This will provide three benefits: 1) reduce microbial loads; 2) remove transient organisms, and 3) provide lot segregation. In cases where wet washes are not used, and not wanted, an alternative method to reduce the microbial load is to apply chlorine dioxide gas as a dry sanitizer. Pure Line has developed a patented chlorine dioxide (CLO2) development process wherein water, as humidity, is absent from the gas. Commissioned research has demonstrated validated log reductions for E. coli along with other food-based pathogens. Current research is ongoing for the application of gas onto or throughout dried products and its ability to reduce the microbial populations. For the plant environment, the CLO2 product can be used on hard surfaces as a sanitizer. For those surfaces that are coated with product, the gas will not be able to penetrate through to the surface beneath without pressure. In these instances, Pure Line has developed a Blower Box that will dispense the gas with pressure.


  1. Derek Mcdoogle says

    I didn’t realize the preventative actions were so important. You mentioned that the corrective action/preventative action, or CAPA, program, works to immediately minimize the risk. I didn’t realize that programs like these were available. Do all companies have CAPA plans that they use?

    • says

      Thank you for your comments. Indeed, preventative controls are an essential part of a food safety program no matter what product is produced. The “immediate” activties, known as corrective actions work to reduce the risk after it is identified. The future or preventative activites work to prevent/minimize the risk in the future. For example, a Corrective Action when a pathogen is identified is to verify that the lot in question is on hold and not distributed to the public. Another corrective action is to perform a cleaning/sanitizing event. A Preventative Action would be to test inbound ingredients through a skip lot testing program and look for trends; work with raw ingredient suppliers on their programs to minimize incoming micro loads; institute a different cleaning/sanitizing regime; redesign equipment so that it will not harbor bacteria; test the environment and look for trends. For each company the CAPA program may have differences, but in general these and other techniques are common throughout the food and ingredient industry.

  2. Bruce Perkin says

    This article does a good job of looking at detection, and treatment to ensure there is a kill step. Are the authors able to advise on what prevention upstream would look like?

    • says

      Thank you for your comment and qustion. Prevention upstream is not easy in dry ingredients or production. A few key components are to 1) veryfy that when grains are cut that they as dry as possible and are maintained or allowed to thoroughly dry while in storage. Moist grains can facilitate microbial growth; 2) Maintain storage silo’s, grain bins, hoses, connections and transport vehicles in clean and dry conditions; 3) Inspect storage silo’s on a consistent basis for cracks, leaks or mildew. Mildew is a indicator of moisture.

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