Escherichia coli (E. coli) is a species of bacteria that belongs to the Enterobacteriaceae family. It is a Gram-negative, rod-shaped bacterium commonly found in the intestines of warm-blooded animals, including humans. While most strains of E. coli are harmless and part of the normal gut microbiota, some can be pathogenic and cause a variety of diseases.

Basic Morphology of E. coli:

• Shape: E. coli is a bacillus (rod-shaped) bacterium.
• Gram Staining: It is Gram-negative, meaning it has a thin peptidoglycan layer in its cell wall and an outer membrane that contains lipopolysaccharides (LPS).
• Size: The typical size of an E. coli cell is about 1–3 micrometers in length and 0.5 micrometers in diameter.


Flagella: E. coli can possess one to several flagella. Flagella are peritrichous (distributed around the cell) and made of the protein flagellin.

Fimbriae (Pili): E. coli often has pili (fimbriae) on its surface. These are hair-like appendages composed of pilin protein. Fimbriae are important for adhesion to host tissues, particularly during infection. They help E. coli adhere to epithelial cells in the human intestine and urinary tract, allowing it to colonize and resist being flushed out by body fluids.

Importance as a Human Pathogen:

Escherichia coli is an important human pathogen, although most strains are harmless and part of the normal gut flora. Pathogenic strains of E. coli can cause various infections, including:


• Gastrointestinal infections: Some strains, especially Enterohemorrhagic E. coli (EHEC), such as the famous strain O157:H7, can cause severe foodborne illness. These strains produce Shiga toxins, which can lead to diarrhea, hemorrhagic colitis, and, in severe cases, hemolytic uremic syndrome (HUS), a potentially life-threatening condition affecting the kidneys.
• Urinary Tract Infections (UTIs): E. coli is the most common cause of UTIs, especially in women. The bacteria can ascend from the urethra to the bladder or kidneys, causing infections. E.coli is responsible for approximately 80–90% of all uncomplicated UTIs. Other bacteria can also cause infections (e.g., Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus saprophyticus) however, none of these are as frequently implicated as E. coli in UTIs.
• Neonatal Meningitis: Certain strains of E. coli, particularly K1 capsular strains, are associated with neonatal meningitis.
• Sepsis: E. coli can also cause systemic infections (sepsis) if it enters the bloodstream, leading to a potentially fatal condition.


In summary, while most E. coli strains are harmless and part of the normal microbiome, certain strains are highly pathogenic and cause significant human diseases, particularly gastrointestinal infections, UTIs, and systemic infections.


Text generated with the help of OpenAI's language model, ChatGPT.