Escherichia coli (ETEC, EHEC)

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Escherichia coli (E. coli) is a gram-negative rod of the enteric tract. Two of the specific E. coli subtypes include Enterohemorrhagic E. coli (EHEC) and Enterotoxigenic E. coli (ETEC). Major microbiology and virulence factors of E. coli include its ability to ferment lactose, K antigen present on the capsule, metallic green sheen on eosin-methylene blue agar (EMB agar), catalase-positive property, and its fimbriae. E. coli is the leading cause of urinary tract infections (UTIs) and gram-negative sepsis. It can also cause meningitis in neonates.

EHEC is most commonly transmitted by consuming undercooked meat and causes bloody diarrhea. It has a unique property of not fermenting sorbitol and produces a Shiga-like toxin that inhibits ribosomes at the 60S position. EHEC can cause hemolytic-uremic syndrome, especially in children under 10. A particular serotype, O157:H7, is associated with EHEC. On the other hand, ETEC is known as traveler's diarrhea and is transmitted via water sources. It produces two toxins: a heat-labile toxin that increases cAMP and a heat-stable toxin that increases cGMP. ETEC causes watery diarrhea instead of bloody diarrhea like EHEC.

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What is the difference between ETEC and EHEC strains of Escherichia coli?

ETEC, or enterotoxigenic E. coli, is a strain of E. coli that produces enterotoxins, causing watery diarrhea and is the most common cause of traveler's diarrhea. EHEC, or enterohemorrhagic E. coli, is another strain that produces Shiga-like toxins, leading to bloody diarrhea and potentially severe complications such as hemolytic uremic syndrome (HUS). EHEC is most commonly associated with the serotype O157:H7.

How is lactose fermentation relevant to the identification of Escherichia coli?

Lactose fermentation is an important characteristic of E. coli, allowing it to be distinguished from other bacteria. E. coli can ferment lactose to produce acid and gas, which results in a change in the appearance of the bacterial colonies when grown on MacConkey's agar. The agar turns pink due to the acid production, indicating a lactose-fermenting bacteria such as E. coli.

How does enterohemorrhagic E. coli (EHEC) cause bloody diarrhea and other complications?

EHEC produces Shiga-like toxins that can cause damage to the lining of the intestine, leading to bloody diarrhea. These toxins can also enter the bloodstream, potentially causing severe complications such as hemolytic uremic syndrome (HUS), which is characterized by hemolytic anemia, thrombocytopenia, and acute kidney injury. EHEC infection is mostly associated with serotype O157:H7, but other serotypes also exist.

What is the connection between Escherichia coli and meningitis?

Certain strains of E. coli, particularly those belonging to the K1 serotype, are known to cause neonatal meningitis. These invasive strains can cross the blood-brain barrier, resulting in inflammation of the meninges and potentially severe neurological complications. It is important to note that meningitis-causing strains are different from the ETEC and EHEC strains that cause gastrointestinal illnesses.