The Hateful Eight: Pathogenic Serotypes of E. coli

While E. coli is naturally found in healthy human and animal intestines, select strains can cause illnesses ranging from diarrhea to UTIs to neonatal meningitis. Learn more about the 8 pathotypes of E. coli, common strains, and the importance of serotyping.

Escherichia coli (E. coli) is a type of bacteria naturally found in the digestive systems of humans and some animals. Although most E. coli are harmless, certain strains are pathogenic and cause disease in humans.

Pathotypes of E. coli

Pathogenic E. coli can be grouped into pathotypes according to their virulence factors and mechanism of causing disease. There are eight main pathotypes of E. coli: ¹

Enteropathogenic E. coli (EPEC)

Enteropathogenic E. coli (EPEC) is a diarrheagenic pathotype of E. coli, meaning it can make you sick with diarrhea. It is spread through ingestion of the bacteria, with the most common routes of infection being contaminated food or water.

The primary symptom of EPEC infection is acute watery diarrhea; however, fever and vomiting may also be present. The incubation period is very short, as symptoms can start appearing as soon as 6 hours after infection.

EPEC is the leading cause of infant diarrhea in developing countries, primarily causing illness in children under 6 months old. EPEC infection is rare in healthy adults due to its high infectious dose, meaning large amounts of the bacteria need to be ingested for infection to occur.²

Enterohemorrhagic E. coli (EHEC)

Enterohemorrhagic E. coli (EHEC) is also diarrheagenic. Also known as Shiga toxin producing E. coli (STEC), it is the most common source of E. coli infection in the United States and Canada due to its low infectious dose. Similarly to EPEC, it is mainly spread through eating contaminated food and beverages and is often implicated in foodborne illness outbreaks. However, EHEC is also easily transmitted from person to person through hand-to-mouth contact.

Infection with EHEC typically presents with watery, then bloody diarrhea, abdominal cramps, and low grade fever. However, 5-10% of EHEC infections may progress to hemolytic uremic syndrome, a severe kidney complication that can be fatal. The incubation period is longer than EPEC, with an average of 3-4 days before symptoms begin appearing. Symptoms typically last for about a week, during which time the bacteria is communicable to others.³

Enterotoxigenic E. coli (ETEC)

Enterotoxigenic E. coli (ETEC) causes “traveler’s diarrhea,” named for its frequency in adults traveling to developing countries. ETEC is primarily spread through the fecal-oral route in areas that lack appropriate sanitation and drinking-water treatment facilities, although it can also be spread through contaminated food.

ETEC infection typically involves mild to moderate watery diarrhea, along with low-grade fever, nausea, and abdominal pain. The incubation period is short at 14-30 hours, and symptoms usually resolve on their own within 2-5 days.⁴

Enteroinvasive E. coli (EIEC)

Enteroinvasive E. coli (EIEC) is a rarer, more severe pathotype of E. coli. EIEC infection causes dysentery, an acute infection of the large intestine which results in watery, sometimes bloody diarrhea, fever, and abdominal cramps. EIEC is typically spread through contaminated food and water, and while person-to-person transmission is rare, it can also occur. Additionally, unlike most other E. coli, EIEC is only found in humans and thus, cannot be spread from animals.

EIEC is rare in the United States and Canada and much less common than ETEC and EPEC in the developing world. The infectious dose is quite high, making EIEC infection most prevalent in children under the age of 5. The incubation period is short, with symptoms appearing as soon as 2 hours after infection.⁵

Enteroaggregative E. coli (EAEC)

Enteroaggregative E. coli (EAEC) can cause both acute and persistent diarrhea⁶ , the latter defined as lasting between 2 and 4 weeks⁷ . Primarily spread through contaminated food and water, it is also the second leading cause of traveler’s diarrhea⁸ . Commonly reported symptoms include watery diarrhea, low-grade fever, abdominal pain, and vomiting. The incubation period has been estimated to be 20-48 hours.⁶

Diffusely adherent E. coli (DAEC)

Diffusely adherent E. coli (DAEC) is the final pathotype of diarrheagenic E. coli. While little is known about DAEC at the moment, it is foodborne and appears to cause childhood diarrhea.⁶

*Interaction of each diarrheagenic E. coli pathotype with a typical target cell*

Uropathogenic E. coli (UPEC)

Uropathogenic E. coli (UPEC) is an extraintestinal pathotype of E. coli, meaning it causes infection outside the intestines.⁹ UPEC is the leading cause of urinary tract infections (UTIs), which occur when bacteria enters the urinary tract through fecal matter, often during sex or while wiping “back to front” after using the washroom. While anyone can contract a UTI, women are at greatest risk due to the proximity of the urethra to the anus.

Symptoms of UTIs include a frequent, strong urge to urinate, a burning sensation during urination, cloudy, bloody, or strong-smelling urine, or pressure in the lower abdomen. UTIs are easily treated with a short course of antibiotics.¹⁰

Neonatal meningitis E. coli (NMEC)

Finally, neonatal meningitis E. coli (NMEC) is another extraintestinal pathotype of E. coli. NMEC can survive in the bloodstream and infect the meninges (protective membranes covering the brain and spinal cord) of newborn infants, causing approximately 20% of cases of neonatal meningitis. However, neonatal meningitis as a whole is rare, occurring in just 2/10,000 full-term infants.¹¹

Without treatment, neonatal meningitis is almost always fatal. Even with treatment, the mortality rate is 5-20%. Symptoms include central nervous system irritation, such as irritation, lethargy, seizures, and vomiting, as well as fever or a bulging fontanelle (soft spot at the top of an infant’s head).¹²

Serotypes of E. coli

Serotypes are distinct groups within a species of bacteria that share similar characteristics. E. coli are serotyped based on three surface antigens, O, H, and K; however, O:H serotyping is considered the gold standard.¹³

The most common pathogenic serotype of E. coli is O157:H7, a type of Shiga toxin producing E. coli (STEC) that is implicated in about 40% of E. coli illnesses in the United States. ¹⁴ However, there are many other STEC serotypes that cause illness, such as O26, O111, O103, O121, O45, and O145. these serotypes appear to be less virulent than E. coli O157:H7, being less likely to cause bloody diarrhea and hemolytic uremic syndrome. ⁶

Another notable serotype of E. coli is O104:H4, which produces Shiga toxins like O157 but also has enteroaggregative characteristics (EAEC). ¹⁵ This serotype was implicated in the 2011 E. coli outbreak in Germany, one of the largest outbreaks of foodborne infections, affecting almost 4000 people and killing 55. ¹⁶

Serotyping of E. coli has many purposes but is especially crucial in outbreak detection and epidemiological surveillance. Understanding the serotype of E. coli that causes an individual’s illness can link cases together in the case of an outbreak, ultimately helping to trace the source of disease. ¹⁴

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