Escherichia coli

Escherichia coli is a gramme-negative, facultative anaerobic, rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms. While most strains are harmless and even beneficial, some serotypes can cause serious food poisoning and other illnesses.

Biology and Biochemistry

E. coli cells are rod-shaped, about 2.0 μm long and 0.25–1.0 μm in diameter. They stain gramme-negative due to a thin peptidoglycan layer and an outer membrane that provides resistance to certain antibiotics. The bacterium employs mixed acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol, acetate, and carbon dioxide.

Metabolism

E. coli can grow on a variety of substrates and uses carbon and energy sources through different pathways. Catabolite repression allows the bacterium to sequentially consume sugars, with glucose being preferred. Optimal growth occurs at 37°C, though some strains can grow at temperatures up to 49°C.

Cell Cycle

The bacterial cell cycle includes three stages: B period (post-cell division to DNA replication), C period (DNA replication), and D period (post-DNA replication to cell division). Fast growth rates result in overlapping cell cycles with multiple replication forks.

Genetic Adaptation

E. coli can transfer DNA via conjugation or transduction, enabling the spread of genetic material. This genetic exchange can lead to the development of pathogenic strains. For instance, the Shiga toxin-producing strain O157:H7 emerged through horizontal gene transfer.

Diversity

E. coli encompasses a wide range of genetic and phenotypic diversity. Genome sequencing reveals that only 20% of genes are shared among all strains. Some strains, like those used in biotechnology (e.g., K-12), differ significantly from pathogenic strains.

Pathogenesis

While most E. coli strains are harmless, pathogenic strains can cause various diseases:

• Gastroenteritis: Symptoms include severe abdominal cramps, diarrhoea, vomiting, and fever. Shiga toxin-producing strains can cause hemorrhagic colitis and hemolytic-uraemic syndrome (HUS), leading to kidney failure and possibly death.
• Urinary Tract Infections (UTIs): Uropathogenic E. coli (UPEC) is a major cause of UTIs.
• Other Infections: Pathogenic strains can also cause neonatal meningitis, sepsis, and pneumonia.

Diagnosis

Diagnosis involves stool cultures and antimicrobial resistance testing. Molecular diagnostic tests can rapidly identify E. coli and its resistance genes. Metagenomics-based platforms are being developed for even faster and more comprehensive diagnostics.

Treatment

The primary treatment includes rehydration and electrolyte replacement. Antibiotics are generally not recommended due to increasing resistance. For traveller's diarrhoea, antibiotics like fluoroquinolones or azithromycin may be used. Rifaximin is effective for non-invasive traveller's diarrhoea.

Prevention

Preventive measures include handwashing, improved sanitation, and safe food handling. Cooking meat thoroughly and avoiding raw, unpasteurized beverages can prevent infections. Vaccine development efforts are focused on Enterotoxigenic E. coli (ETEC).

Role in Biotechnology

E. coli is widely used in biotechnology for the production of recombinant proteins, including human insulin. Its ability to quickly grow and be easily manipulated makes it an ideal model organism for genetic studies.

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Self-assessment MCQs (single best answer)

What is the shape of Escherichia coli cells?

Which of the following is NOT a product of E. coli's mixed acid fermentation?

At what optimal temperature does E. coli typically grow?

What significant process allows E. coli to transfer DNA and potentially spread pathogenic traits?

Which strain of E. coli is known for producing Shiga toxin?

What type of infections is Uropathogenic E. coli (UPEC) primarily associated with?

Which diagnostic method is NOT mentioned as being used to identify E. coli and its resistance genes?

What is the primary treatment recommended for E. coli infections?

Which preventive measure is NOT mentioned as a way to avoid E. coli infections?

In biotechnology, what is a common use for E. coli?