About E. coli

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About E. coli Blog

Pre-Washed Salad

Leisa Zigman, Investigative Reporter for KSDK, did a story on pre-washed salad:
For busy, health conscious people, pre-washed and bagged salads are a huge time saver. Just open and eat. But did you ever wonder how well it’s washed? Investigative Reporter Leisa Zigman did, so she had the salad tested.
Busy mom Susan Stern uses the bagged lettuce about once a week, “It’s all about saving time. It’s already chopped, already prepared. I don’t have to clean it. I don’t have to do anything but open the bag.”
Two weeks ago, we randomly bought three bags from three different stores. The bags were Fresh Express European Mix, Fresh Express Spinach, and Earthbound Farm Organic.
The Fresh Express said “thoroughly washed.” Earthbound Farm Organic salad claimed it was triple washed.
Scientists at Microbe Innotech in Bridgeton analyzed the samples. Lab Manager Andrew Johnson found the organic mix had 21,300,000 bacteria colonies inside the entire bag. He found more than 3,000 colonies were coliform bacteria or e-coli like.


The Fresh Express European he said was the cleanest with zero coliform bacteria. Johnson also said the Fresh Express Spinach had the highest coliform count, 143,000 bacteria in the bag.
Johnson said, “It seemed like that was pretty rampant with bacteria.”
A spokesperson with Fresh Express said, “It’s not surprising to find bacteria on fresh produce because bacteria is naturally occurring in soil and on plants.” The spokesperson went on to say the bacteria was not harmful and wouldn’t make a person sick.
A spokesperson with the International Fresh Cut Produce Association said, “The vast majority of coliforms are not harmful to humans … and some bacteria is beneficial.”
Johnson said this report has changed his eating habits, “I come home and throw it in the dish and throw on salad dressing. I probably won’t do that now. I would probably wash it off now and be more cautious of it.”
Even if you do wash it yourself, Johnson said, you’d never get rid of all the bacteria.
Stern said, “I’ll still buy it that way because it’s chopped and it’s a time saver. But I’ll wash it, and stick it in a colander.”
The Fresh Cut Produce Association stressed it’s not necessary to wash already washed lettuce. If you do, make sure to use a clean colander, salad spinner, or clean paper towels. A Earthbound Farm Organic spokesperson tells Newschannel 5 that in 20 years there has never been a food borne illness associated with its product.
Experts from University of California-Berkeley and Tufts University researched the salad bacteria as well.
Microbiologists concluded the companies’ mechanical washing is better than what consumers can do at home. They advised consumers to be sure the package is sealed, dated and labeled “pre-washed” and/or “ready to eat.” Don’t use greens after the expiration date, it advises.
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The following is reprinted from the Fresh Cut Produce Association:
Frequently Asked Questions about Microbes and Fresh-cut Produce
1. Are microbes on salads, fruits and vegetables dangerous to humans?
Fruits and vegetables are grown outdoors in or near soil, water and air, all of which have microorganisms associated with them. Most bacteria commonly found on produce are harmless to humans and they are nearly impossible to wash off completely. Some harmless bacteria play a useful role in causing produce to spoil, signaling to humans that food is no longer good to eat. Even when these “good” microbes reach high levels on produce, they do not necessarily signal a food safety problem and there are currently no government limits for the presence of these harmless bacteria because counts of these bacteria do not correlate with food safety.
2. What about coliform bacteria?
It is no surprise to find coliform bacteria on fruits and vegetables. Coliform bacteria encompass a wide variety of microbes that are commonly associated with the soil and are naturally part of the microbial population found on roots, leaves, flowers, and fruits of produce as well as edible crops grown in every home garden. Coliform bacteria are routinely used as indicator organisms to test the safety of water, milk, or heat-treated foods to confirm that the process used to remove pathogens was adequate. Since fresh produce is not cooked, coliforms are generally found on these products. The presence of coliforms on fresh produce does not necessarily indicate that it was grown, held, or processed under unsanitary conditions nor do they indicate any specific food safety risk.
3. What about generic E. coli bacteria?
Generic E. coli is a subgroup of nonpathogenic coliforms and may occasionally be found on fresh produce in low numbers. Generic E. coli does not cause illness and only a few special types or “strains” of E. coli are harmful to humans. The presence of generic E. coli of fresh produce does not definitively mean that produce is contaminated with harmful bacteria.
4. What tests are used to look for bacteria on produce?
Bacteria are too small to be seen without the use of a microscope, hence the term microorganism. Counting under high magnification is extremely tedious and most bacteria do not have distinct features that allow us to identify them visually. For these reasons, we use general or specialized nutrients and enzyme reactions to both count and tentatively identify groups of bacteria by their common traits. Total Plate Count (TPC or Aerobic Plate Count, APC) tests, Total Coliform tests and E. coli tests are most commonly used to analyze fruits and vegetables.
Total Plate Count (TPC) or Aerobic Plate Count (APC) estimates general bacterial residents on fruits and vegetables. In reality, only 10-20% of total bacteria associated with plants and soil can be cultured in this way. Produce packagers use TPCs to help track changes in microbial populations throughout the product’s shelf life. Invariably, these numbers will increase throughout the life of the product, even under refrigeration. Numbers derived from TPCs-even up to a million cfu (colony forming units) per gram of product-do not necessarily indicate a significant impact on quality or taste and certainly are not predictive of a food safety risk.
Total Coliform tests indicate the presence of members of the Enterobacteriaceae family.. Most coliforms found on fresh produce are non-pathogenic bacteria commonly found in the soil, in water, and on all plant surfaces regardless of where they are grown. The vast majority of coliforms are not harmful to humans. Testing for coliform bacteria on fresh produce is not a good measure of food safety. Coliform standards for water, dairy and other foods cannot be meaningfully applied to fresh-cut produce.
Fecal Coliform or Thermotolerant Coliform tests zero in on those coliform bacteria that can grow at temperatures at or somewhat higher than the human body (98.6 to 108oF). Fecal coliforms are generally recognized as residents of the intestinal tracts of animals but the majority can form natural associations with plants. Others that have no recognized in animals will also be identified as fecal or thermotolerant coliforms. Thermotolerant coliforms are generally found on fresh produce in low numbers and do not definitively indicate poor quality or unsanitary handling or processing practices. E. coli will also give a positive reaction in fecal coliform tests. Only a few E. coli sub-species like O157:H7 are harmful to humans. Care should be taken to correctly identify them before raising a food safety alarm.
5. Are bacteria referred to in recent news stories harmless?
Yes! In every case the lab tests that were conducted tell us nothing about food safety nor the potential presence of true pathogens, that would be cause for concern. The bacteria naturally found on produce are not only harmless but also beneficial to the human body. These good bacteria, like those found in yogurt, are important because they may actually help reduce the growth of harmful bacteria in the event that unintentional contamination or cross contamination occurs.
6. Should consumers wash packaged salads or fresh-cut fruits and vegetables before eating them?
Packaged salads or fresh-cut fruits and vegetables are washed and dried before packaging under sanitary conditions. If a package says “washed” or “washed and ready to eat” or “triple washed,” there is no need to rewash the product before eating. To assure the best quality and enjoyment, be sure to check the date coded on the package, usually indicated by a phrase such as “use by,” “best if used by” or “enjoy by.” If you decide to wash fresh-cut products to re-crisp them you should take care not to do so in an environment that could contaminate them. Use a clean colander to wash with running water and dry in a clean salad spinner or with clean paper towels. FDA’s first rule of food preparation is “keep everything clean.”

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