Morphology of E. coli

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Last Updated on January 13, 2020 by Sagar Aryal

Morphology of E. coli

  1. E. coli is gram-negative (-ve) rod-shaped bacteria.
  2. It is 1-3 x 0.4-0.7 µm in size and 0.6 to 0.7 µm in volume.
  3. It is arranged singly or in pairs.
  4. It is motile due to peritrichous flagella.
  5. Some strains are non-motile.
  6. Some strains may be fimbriated. The fimbriae are of type 1 (hemagglutinating & mannose-sensitive) and are present in both motile and non-motile strains.
  7. Some strains of E. coli isolated from extra-intestinal infections have a polysaccharide capsule.
  8. They are non-sporing.
  9. They have a thin cell wall with only 1 or 2 layers of peptidoglycan.
  10. They are facultative anaerobes.
  11. Growth occurs over a wide range of temperatures from 15-45°C.

Morphology of E. coli

Antigenic Structure

  1. Heat Stable Lipopolysaccharide (LPS) is the major cell wall antigen of E. coli.
  2. E. coli possesses 4 antigens; H, O, K and F.

H or Flagellar Antigen

  • Heat and alcohol labile protein
  • Present on the flagella
  • Genus specific
  • Present as monophasic
  • 75 ‘H’ antigens have been recognized

O or Somatic Antigen

  • Heat stable, resistant to boiling up to 2 hrs. 30 minutes
  • Occur on the surface of the outer membrane
  • An integral part of the cell wall
  • 173 ‘O’ antigens have been recognized

K or Capsular Antigen

  • Heat labile
  • Acidic polysaccharide antigen present in the envelope
  • Boiling removes the K antigen
  • Inhibit phagocytosis
  • 103 ‘K’ antigens have been recognized

F or Fimbrial Antigen

  • Heat labile proteins
  • Present in the fimbriae
  • K88, K99 antigens


  1. Subhash Chandra Parija. Textbook of Microbiology & Immunology.
  2. Ananthanarayan and Paniker. Textbook of Microbiology.
  3. Topley and Wilson’s Microbiology and Microbial Infection. Bacteriology Volume 2. Part VI. Organisms and their biology. Chapter 36. Escherichia, 1360.
  4. Bailey and Scott’s Diagnostic Microbiology. Part 3. Section 7. Chapter 22. Enterobacteriaceae, 323.
  5. Mackie and McCartney Practical Medical Microbiology. Section B. Bacteria and Related Organisms. Chapter 20. Escherichia, 361.

Morphology of E. coli

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