Escherichia coli (E. coli) is a diverse group of bacteria found in humans' and animals' environments, food, and intestines. Although this group of bacteria is known for being associated with foodborne illnesses, most strains of E. coli are harmless and are part of the normal human microbiome. Read on to learn about the differences between the beneficial and pathogenic strains of E. coli.
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What Is Escherichia coli?
Belonging to the Enterobacteriaceae phylum, E. coli is a Gram-negative facultative anaerobe, meaning that, unlike other types of probiotic bacteria, it can live in environments with or without oxygen. Humans are typically exposed to E. coli by maternal transmission during birth, through exposure to the mother's fecal matter and subsequent handling. (1)
Many bacterial strains belong to the E. coli species, most of which are harmless and normal commensal inhabitants of the gastrointestinal tract. There are six pathogenic strains of E. coli that are known to cause diarrhea, which include (2):
- Shiga toxin-producing E. coli (STEC)/Enterohemorrhagic E. coli (EHEC): This is the bacteria most commonly associated with E. coli food contamination and diarrhea. E. coli O157 is the strain of STEC that most frequently causes diarrheal illness in North America by producing a toxin called Shiga, which can affect the small intestine's lining.
- Enterotoxigenic E. coli (ETEC): This strain is a common cause of travelers' diarrhea.
- Enteroaggregative E. coli (EAEC)
- Enteroinvasive E. coli (EIEC)
- Enteropathogenic E. coli (EPIC)
- Diffusely adherent E. coli (DAEC)
What Is Escherichia coli's Role in the Gut Microbiome?
Beneficial strains of E. coli may help produce vitamins B12 and K, consume oligosaccharides and simple sugars, and ferment amino acids. E. coli consumes oxygen, which can help maintain a suitable environment for the beneficial microbes of the gut microflora that are strictly anaerobic (bacteria that cannot grow when oxygen is present). (1, 3)
The presence of beneficial E. coli strains may help support intestinal health by competitively excluding pathogenic agents from binding to epithelial binding sites. E. coli Nissle 1917 (EcN) is one probiotic strain of E. coli that has been studied for its potential to support the intestinal barrier and overall gut health. (4, 5)
What Are the Health Consequences of Unbalanced Escherichia coli in the Gut Microbiome?
Some E. coli species are pathobionts, opportunistic microbes that can stimulate inflammatory immune responses and may contribute to health issues. E. coli is a producer of hydrogen sulfide (H2S) and ethanol and, as such, may influence intestinal permeability when present in large amounts. (3, 6)
Both commensal and pathogenic E. coli strains can produce biofilms, assemblies of microbial cells enclosed in bacterial-produced matrixes of polysaccharides and proteins. Biofilms are associated with increased infection chronicity and severity because they may help pathogens evade host immune defenses and resist antibiotic intervention. (7, 8)
Some studies have suggested a potential link between E. coli and the development and severity of inflammatory bowel disease, especially Crohn's disease (9).
What Causes Low Levels of Escherichia coli?
A study on 250 vegetarian and vegan individuals concluded that fecal E. coli levels were lower in groups with lower stool pH, as seen in patients eating higher carbohydrate and fiber diets. (13)
The intake of prebiotics (FOS, GOS, inulin, and lactulose) and probiotics (fermented foods and dietary supplements) has been shown to beneficially modulate the gut microbiome composition so that it favors beneficial Lactobacillus and Bifidobacteria and may reduce E. coli. (10, 11)
What Causes High Levels of Escherichia coli?
Dietary choices can influence the growth of E. coli within the intestines, as shown by studies that found higher fecal E. coli levels in patients eating more animal protein and gluten-free diets. (13, 14)
E. coli infection can occur from eating contaminated food, drinking contaminated water, or personal contact (fecal-oral transmission). The most common contaminated food sources of E. coli include ground beef, unpasteurized milk, and fresh produce. (2, 12)
Symptoms of Escherichia coli Infection
Ingestion of pathogenic E. coli strains, even in small amounts, can lead to infection, characterized by the following symptoms (2, 12):
- Diarrhea, ranging in severity from mild to severe and bloody
- Stomach pain and cramping
- Nausea and vomiting
- Loss of appetite
- Fever
- Fatigue
Hemolytic uremic syndrome (HUS) is a potential complication of STEC that may develop on average seven days after the first symptoms of E. coli infection. HUS occurs when Shiga toxin enters the bloodstream, affects red blood cells and platelets, and may cause kidney damage. HUS can be serious and develops in 5-10% of patients infected with STEC. Children five years and younger are at the highest risk of this health complication. Symptoms of HUS include (2):
- Bloody diarrhea
- Fever
- Abdominal pain
- Vomiting
- Decreased urination, blood in the urine
- Pale skin with easy bruising
- Increased heart rate
- Fatigue
- Lightheadedness, confusion, seizures
- Kidney issues
How to Test Escherichia coli Levels
Functional labs can help measure commensal E. coli of the gut microbiome and identify pathogenic E. coli presence.
Comprehensive Stool Test
Comprehensive stool tests use various technologies, such as stool culture and polymerase chain reaction (PCR), to identify the growth of beneficial E. coli. Genova Diagnostic's GI Effects Profile is an example of a comprehensive stool test frequently ordered by functional medicine providers. Genova offers an add-on enterohemorrhagic E. coli test to screen for pathogenic STEC presence as warranted by patient symptoms.
The GI-MAP test by Diagnostic Solutions is another popular comprehensive stool panel that extensively screens for the various pathogenic E. coli strains and Shiga toxin.
E. coli Shiga Toxins
Identification of E. coli presence can be made by measuring the presence of Shiga toxin in stool. Generally, a positive Shiga toxin test is confirmed by follow-up fecal testing for E. coli O157.
How to Address Escherichia coli Presence
Addressing E. coli presence largely depends on bacterial strain and severity of symptoms. Symptomatic management is a mainstay of both conventional and functional approaches, with oral and/or IV rehydration and antidiarrheals, like bismuth subsalicylate or loperamide. Antibiotics may be considered for severe symptoms, but due to the increased risk of HUS, they are not indicated for patients with suspected or confirmed EHEC/STEC. (15)
Herbal antimicrobials can be considered as an alternative to prescription antibiotics when appropriate. Hydrastis canadensis or Berberis aquifolium are sometimes used as potent antimicrobials and intestinal tonics. One clinical trial suggested that a single oral dose of 400 mg of berberine may help reduce stool volume in patients with ETEC presence and that 42% of patients were asymptomatic (compared to only 20% of controls) within 24 hours.
Activated charcoal is sometimes used as an adsorber of E. coli toxins, potentially reducing small intestinal damage and gastrointestinal symptoms associated with the presence of the bacteria.
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Summary
E. coli is a bacteria found naturally in the human gastrointestinal tract. While many strains of E. coli are part of a healthy gut, an overgrowth can be associated with bowel inflammation, and the presence of specific strains can be linked to diarrhea and other health issues. Functional testing can help analyze intestinal E. coli presence. An integrative approach to gut health may help manage E. coli presence and support overall well-being.
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