What kind of bacterium is Escherichia coli?

  1. coli was first discovered in 1885 by a German bacteriologist named, Theodor Escherich.

The Escherichia coli genus contains 5 different species:

  • Escherichia coli,
  • Escherichia fergusonni,
  • Escherichia hermanii,
  • Escherichia vulneris, and
  • Escherichia blattae.

From the above mentioned species, Escherichia coli is the most common species.

Escherichia coli is a Gram – negative, rod-shaped bacteria, with an aerobic and anaerobic growth. These bacteria are commonly found in animal species and lower intestines of mammals. The optimal temperature for Escherichia Coli to grow is 37 degrees. Some laboratory strains can multiply in temperatures up to 49 degrees. They do not form spores. This means that they are easily killed basic sterilization or boiling. These bacteria normally live in the human’s gastrointestinal tract. Most strains are harmless; however, some such as O157:H7 can cause food poisoning in humans.

Cells are typically about 2 micrometer long and 0.5 micrometer, in diameter, with a cell volume of 0.6 – 0.7 m3.

Escherichia Coli possesses adhesive fimbriae. The cell walls of this bacterium consist of an outer membrane, a periplasmatic space and an inner membrane. The outer membrane contains lypopolysaccharides. The periplasmatic space has a peptidoglycan layer, while the inner membrane is an cytoplasmic membrane. Even though it has extremely simple cell structure, with only one chromosomal DNA and a plasmid, it can perform complicated metabolism to maintain its cell growth and cell division. Escherichia coli is able to produce soluble amyloid oligomers. Escherichia coli colonies are relatively big, with regular borders.

  1. coli possesses the ability to transfer DNA via bacterial conjugation, transduction or transformation, which allows genetic material to spread horizontally through an existing population. This process leads to the spread of the gene encoding shiga toxin from Shigella to Escherichia coli.

Only 20 % of the genome is the same at all the strains of Escherichia Coli. The genome structure of Escherichia Coli is characterized by one circular chromosome. The chromosomal DNA of Escherichia Coli has been completely sequenced. 70% of chromosomes are monocistronic, while 6% are polycistronic. This means that 70% of chromosomes are composed by single genes, while 6% of chromosomes are composed by double genes.

Escherichia coli is lactose positive, but is also able to ferment glucose, dextrose, forming acids with or without gas. They do not produce H2S. Some strains produce lethal toxins. Some strains are piliated and capable of accepting and transferring plasmid to and from other bacteria.

Different strains of E. coli can be found in different type of animals. Today, with examination of the strain of Escherichia coli found in the stool, which has caused the infection, we are able to determine if the infection results from humans or from animals.

The antigenic structure of Escherichia coli is very complex. Escherichia coli is characterized by more than 170 O antigens, 56 H antigens and more than 80 K antigens.

Within 40 hours of birth the gastrointestinal tract of infants is colonized by Escherichia Coli, which adheres to the mucus of the large intestine and remains non pathologic.

Escherichia coli is also commonly used as an indicator in the field of water purification.

Escherichia coli

Diarrhea caused by Escherichia coli

Among the many strains of E. coli, only a few trigger diarrhea. One group of E. coli — which includes O157:H7. This type of Escherichia Coli produces a powerful toxin, which is able to damage the lining of the small intestine. The damage of this lining of the small intestine’s, causes a bloody diarrhea. Only few bacteria are required for the infection to occur.

People usually get infected with Escherichia coli while consuming contaminated food, contaminated water, or with a personal contact to a person, which is infected. Escherichia coli can be easily transmitted from one person to another, especially when they don’t wash their hands regularly.

Everyone has the risk to get infected with this kind of bacteria. People who are at a greater risk to get infected include:

  • Infants, young children, elderly adults
  • Compromised immune system – like in HIV/AIDS, organ transplants, etc.
  • Consuming some types of food – unpasteurized milk and other dairy products, undercooked meat, hamburgers, apple juice, soft cheese, etc.
  • Time of the year – the infections with Escherichia Coli are more likely to occur in spring and summer, from June through September.

Most adults recover from an Escherichia Coli infection, within one week without any complications. However, life threatening complications may develop in infants, young children and elderly people. These complications include kidney failure and hemolytic uremic syndrome.

Escherichia coli infection typically begins three to four days after the exposure to the bacteria. However, the signs and symptoms may appear as soon as one day or even after more than one week after exposure.

Signs and symptoms include a mild, moderate or severe diarrhea, bloody diarrhea, nausea, vomiting, abdominal cramps, abdominal pain, tenderness of the abdomen, etc.

How is an Escherichia Coli infection diagnosed?

Escherichia Coli is diagnosed from samples of the stool, taken for laboratory tests. These tests will help identify the presence of Escherichia Coli bacteria. The bacteria may be cultured to confirm the diagnosis and identify specific toxins, such as those produced by E. coli O157:H7.

For infections caused by Escherichia Coli there is no proper treatment. No treatment can cure the infection, relieve the symptoms or prevent possible complications. Treatment usually includes bed rest and fluids to prevent dehydration.

Anti – diarrheal preparations like Loperamide are not recommended, because they can worsen the situation.

Hospitalization is needed in serious forms of infections, when complications like kidney failure or hemolytic uremic syndrome occur. Supportive therapy with intravenous fluids, blood transfusions and even dialysis in cases with kidney failure are necessary.

There is no vaccine or medication against infections with Escherichia Coli.

Prevention is the best way of avoiding infections. Personal hygiene, washing the hands, cooking the food properly, washing the fruits and vegetables, avoiding to drink unpasteurized milk and other dairy products like yogurt, cheese, apple juice, cider, etc.