Shiga toxin-producing Escherichia coli (STEC)


Escherichia coli (E. coli) is a large and diverse group of bacteria that normally live in the intestines of humans and animals. Most strains of E. coli are harmless or even beneficial, but some can cause serious illness by producing toxins that damage the cells lining the intestines and other organs. These strains are called Shiga toxin-producing E. coli (STEC) because they produce a type of toxin called Shiga toxin.

Shiga toxin was first discovered in Shigella dysenteriae, a bacterium that causes dysentery, a severe form of diarrhea with blood and mucus in the stool. Shiga toxin is composed of one A subunit and five B subunits, which bind to specific receptors on the surface of host cells. The A subunit then enters the cell and blocks protein synthesis, leading to cell death.

There are many different types of STEC, which are classified by their O and H antigens on their surface. The most common and well-known type is E. coli O157:H7, which was first identified as a cause of human disease in 1982 after an outbreak of bloody diarrhea linked to contaminated hamburgers. However, other types of STEC, such as O26, O45, O103, O111, O121, and O145, can also cause severe illness and are sometimes referred to as non-O157 STEC.

STEC infections can range from mild diarrhea to hemorrhagic colitis (HC), a condition characterized by severe abdominal cramps and bloody diarrhea. In some cases, especially in children under five years of age and the elderly, STEC infections can lead to a life-threatening complication called hemolytic uremic syndrome (HUS), which involves kidney failure, low platelet count, and hemolytic anemia.

STEC infections are usually acquired by eating or drinking contaminated food or water, such as undercooked ground beef, raw milk, unpasteurized juice, or fresh produce. The bacteria can also be transmitted from person to person through poor hygiene or contact with animals or their feces. It takes only a small number of bacteria (less than 100) to cause infection. The symptoms usually appear within 3 to 4 days after exposure but can range from 1 to 10 days.

STEC infections are diagnosed by testing stool samples for the presence of the bacteria or their toxins. Treatment is mainly supportive, as antibiotics are not effective and may increase the risk of HUS. Fluid replacement and electrolyte balance are important to prevent dehydration and complications. In cases of HUS, hospitalization and dialysis may be required.

STEC infections are preventable by following good food safety practices, such as cooking meat thoroughly, washing fruits and vegetables before eating, avoiding raw or unpasteurized dairy products and juices, and washing hands frequently with soap and water.