E. coli: Full of Crap?

What comes to mind when you hear about E. coli? Most likely, you associate E. coli with food poisoning or a bad meal. Maybe a trip to Chipotle took a wrong turn. Indeed, the Centers for Disease Control and Prevention reports that ~75,000 people become ill each year in the U.S. from the particular strain called E. coli O157:H7.¹ However, you might not know that there are hundreds of strains of E. coli, and most strains are harmless! In fact, this bacteria is vital to the science community, and has been researched extensively, to our great benefit!²

E. coli: The Good

E. coli, or Escherichia coli, is found in 90% of humans, growing naturally in the intestines.³ It helps promote a balance of healthy bacteria against pathogenic bacteria by depriving harmful bacteria of nutrients and space. It also changes the environment by lowering the pH or by other mechanisms, which makes it harder for pathogenic bacteria to reside in the gut. Additionally, it  synthesizes vitamins essential for our body.⁴ 

E. coli is a model organism, which is an organism that is studied substantially to provide insight into characteristics or biological processes of other organisms.⁵ E. coli is a terrific model organism because it grows quickly in the lab and can be easily cultured, which cannot be said about most bacteria or other animals. In 1978, David Goeddel and his colleagues at Genentech were the first to successfully insert the insulin human gene into E. coli by using a method that combines two pieces of DNA together to generate a new strand of DNA called recombinant DNA. As a result, the bacteria were able to produce human insulin.^{6, 7} Since this discovery, E. coli has been genetically engineered to produce human insulin for the treatment of diabetes.

Researchers at the University of Colorado at Boulder discovered that E. coli also plays a beneficial role in producing a compound that takes up iron. As a result, the bacteria could potentially be used to treat people with iron deficiency anemia, a condition that affects more than 1 billion people worldwide. Min Han, a professor in the Molecular, Cellular and Developmental Biology department, acknowledges that oral iron supplements may backfire and reduce iron absorption, so E. coli may provide a more effective treatment for those with iron deficiency.⁸

E. coli is essential in humans and has played an important role in research and in medical advancements.

When E. coli Goes Rogue

Even though most strains of E. coli are harmless, some strains can acquire virulence factors through plasmids or bacteriophages, which introduce new genetic material into the cell. Some of that genetic material carried over may produce pathogenic toxins, resulting in infections and disease.⁹ This is  the case for E. coli O157:H7.

The strain of E. coli most commonly associated with food poisoning is E. coli O157:H7, also known as enterohemorrhagic E. coli, or EHEC.⁹ This strain carries an extra gene that codes for Shiga toxin, which will damage the host cell. E. coli O157:H7 also has acid resistance, so it can survive in the acidic stomach and can therefore colonize the intestine and cause infection.^{9, 10} 

The strain of E. coli most commonly associated with food poisoning is E. coli O157:H7, also known as enterohemorrhagic E. coli, or EHEC.

As many as 10 viable bacteria can cause disease, and when a person ingests contaminated meat, dairy, or greens, then a special set of genes help EHEC bind to epithelial cells, the cells that line the intestine and are responsible for nutrient absorption. When the Shiga toxin is delivered to these cells, it causes lesions. The toxin cleaves ribosomal RNA, a molecule that helps synthesize proteins. As a result, the toxin disrupts protein synthesis necessary for cell maintenance and normal intestinal cell function, which may lead to blood in stool.^{10, 11} 

When the Shiga toxin travels through the bloodstream and binds to kidney cells, it intoxicates them, which may result in hemolytic uremic syndrome.^{9, 10} Hemolytic uremic syndrome can cause clot formation in the kidney blood vessels, affecting the filtering system and potentially causing kidney failure. 

However, the good thing about food infection with EHEC is that it is self limiting, meaning that the infection can be cleared without the need for medicine such as antibiotics.¹⁰ Even though it may cause hemolytic uremic syndrome, this disease is uncommon, affecting up to 10% of people with EHEC infection. While it tends to affect young children and the elderly at higher rates, for most people, it is not fatal.¹² However, everyone can and should take precautions to prevent food infection.

Conclusion

E. coli is a remarkable organism that has helped advance scientific knowledge and create medical treatments for people. However, the bacteria also plays a huge role in food poisoning, which is not fun to experience or think about.

To help prevent food infections, the CDC states and recommends:

• EHEC is heat sensitive, so cook meat thoroughly. Use a food thermometer to make sure that meat is at a safe temperature for consumption.
• Thoroughly wash your hands and cooking surfaces after they touch raw meat. Wash vegetables thoroughly.
• If dealing with cattle, be aware of fecal contamination. EHEC originated from cattle, goat, deer, and sheep intestines, so feces may contain E. coli O157:H7.¹³

References

1. Rangel, J. M., Sparling, P. H., Crowe, C., Griffin, P. M., & Swerdlow, D. L. (2005). Epidemiology of Escherichia coli O157:H7 outbreaks, United States, 1982-2002. Emerging infectious diseases, 11(4), 603–609. https://doi.org/10.3201/eid1104.040739
2. Blount Z. D. (2015). The unexhausted potential of E. coli. eLife, 4, e05826. https://doi.org/10.7554/eLife.05826
3. Delmas J, Dalmasso G, & Bonnet R. (2015). Escherichia coli: The Good, the Bad and the Ugly. Clin Microbiol 4: 195. doi: 10.4172/2327-5073.1000195
4. Johns Hopkins Medicine. (n.d.). Escherichia coli O157:H7. https://www.hopkinsmedicine.org/health/conditions-and-diseases/escherichia-coli-o157-h7
5. The Public Engagement team at the Wellcome Genome Campus. (2020). What are model organisms? https://www.yourgenome.org/facts/what-are-model-organisms. 
6. U.S. National Library of Medicine. (n.d.). How did they make insulin from recombinant dna? https://www.nlm.nih.gov/exhibition/fromdnatobeer/exhibition-interactive/recombinant-DNA/recombinant-dna-technology-alternative.html
7. Quianzon, C. C., & Cheikh, I. (2012). History of insulin. Journal of community hospital internal medicine perspectives, 2(2), 10.3402/jchimp.v2i2.18701. https://doi.org/10.3402/jchimp.v2i2.18701
8. The unexpected upside of E. coli. CU Boulder Today. (2018, August 27). https://www.colorado.edu/today/2018/08/22/unexpected-upside-e-coli#:~:text=Best%20known%20as%20a%20pathogen,new%20CU%20Boulder%20research%20shows. 
9. Lim, J. Y., Yoon, J., & Hovde, C. J. (2010). A brief overview of Escherichia coli O157:H7 and its plasmid O157. Journal of microbiology and biotechnology, 20(1), 5–14.
10. Ottemann, K. (2020). [METX119L Lecture Content]
11. Ameer, M., Wasey, A., & Saleen, P. (2021, February 11). Escherichia coli (E coli 0157 H7). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK507845/
12. World Health Organization. (2018, February 7). E. coli. https://www.who.int/news-room/fact-sheets/detail/e-coli
13. Centers for Disease Control and Prevention. (2020, June 09). E. coli and food safety. https://www.cdc.gov/foodsafety/communication/ecoli-and-food-safety.html