What Are the Different Strains of E. Coli?

Posted in E. coli on May 26, 2026

There are many different strains of E. coli, ranging from harmless bacteria to dangerous pathogens capable of causing severe illness. STEC strains like E. coli O157:H7 are among the most serious because they can cause bloody diarrhea and kidney complications, while other strains are linked to traveler’s diarrhea, UTIs, and infant infections.

Shiga Toxin-Producing E. Coli (STEC)

STEC strains are among the most dangerous types of E. coli because they produce powerful toxins known as Shiga toxins. Common STEC strains include:

• E. coli O157:H7

• E. coli O26

• E. coli O45

• E. coli O103

• E. coli O111

• E. coli O121

• E. coli O145

These strains are mostly linked to undercooked beef, leafy greens, raw milk, and contaminated water. Symptoms often include severe stomach cramps, bloody diarrhea, and vomiting. Some infections can lead to Hemolytic uremic syndrome (HUS), a potentially life-threatening condition that can cause kidney failure.

E. Coli O157:H7

E. coli O157:H7 is the most well-known STEC strain and one of the leading causes of severe foodborne illness outbreaks. This strain is particularly dangerous because:

• It produces strong Shiga toxins.

• Even small amounts can cause illness.

• It frequently causes bloody diarrhea and serious complications.

Outbreaks involving O157:H7 are often associated with contaminated beef, produce, and unpasteurized products.

Enterotoxigenic E. Coli (ETEC)

ETEC strains are a common cause of traveler’s diarrhea and are a major source of diarrheal illness worldwide. These strains spread through contaminated food and unsafe drinking water. Symptoms usually include watery diarrhea, stomach cramps, and nausea. ETEC infections are generally less severe than STEC infections but can still wind up causing significant dehydration.

Enteropathogenic E. Coli (EPEC)

EPEC strains primarily affect infants and young children. These strains attach to the intestinal lining and interfere with normal absorption. Common symptoms include:

• Persistent diarrhea

• Vomiting

• Fever in some cases

EPEC infections are more common in areas with poor sanitation and limited access to clean water.

Enteroaggregative E. Coli (EAEC)

EAEC strains form dense bacterial layers along the intestinal wall. Symptoms may include persistent diarrhea, abdominal pain, and nausea. These infections can last longer than other types of E. coli illness and may be especially serious in young children or immunocompromised individuals.

Enteroinvasive E. Coli (EIEC)

EIEC strains invade and damage intestinal cells in a way similar to Shigellosis. Symptoms often include fever, stomach cramps, and bloody diarrhea. These infections are less common in the U.S.

Diffusely Adherent E. Coli (DAEC)

DAEC strains attach to intestinal cells in a diffuse pattern and are associated with diarrhea, particularly in children. Some infections are mild while others are prolonged. Researchers continue studying DAEC because its role in illness is less understood and symptoms can vary widely.

Uropathogenic E. Coli (UPEC)

Not all harmful E. coli strains cause food poisoning. UPEC strains are a leading cause of urinary tract infections (UTIs). These strains can spread from the digestive tract into the urinary system and cause kidney infections in severe cases. UPEC infections are especially common in women.

Neonatal Meningitis-Associated E. Coli (NMEC)

NMEC strains are rare but dangerous because they can cause meningitis in newborns. These infections may lead to:

• Brain inflammation

• Seizures

• Serious neurological complications.

Swift medical treatment is critical.