Morphology of E. coli
- E. coli is gram negative (-ve) rod shaped bacteria.
- It is 1-3 x 0.4-0.7 µm in size and 0.6 to 0.7 µm in volume.
- It is arranged singly or in pairs.
- It is motile due to peritrichous flagella.
- Some strains are non-motile.
- Some strains may be fimbriated. The fimbriae are of type 1 (hemagglutinating & mannose-sensitive) and are present in both motile and non-motile strains.
- Some strains of E. coli isolated from extra-intestinal infections have polysaccharide capsule.
- They are non-sporing.
- They have thin cell wall with only 1 or 2 layers of peptidoglycan.
- They are facultative anaerobes.
- Growth occurs over a wide range of temperature from 15-45°C.
- Heat Stable Lipopolysaccharide (LPS) is the major cell wall antigen of E. coli.
- E. coli possess 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 upto 2 hrs. 30 minutes
- Occur on surface of outer membrane
- 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
- Subhash Chandra Parija. Textbook of Microbiology & Immunology.
- Ananthanarayan and Paniker. Textbook of Microbiology.
- Topley and Wilson’s Microbiology and Microbial Infection. Bacteriology Volume 2. Part VI. Organisms and their biology. Chapter 36. Escherichia, 1360.
- Bailey and Scott’s Diagnostic Microbiology. Part 3. Section 7. Chapter 22. Enterobacteriaceae, 323.
- Mackie and McCartney Practical Medical Microbiology. Section B. Bacteria and Related Organisms. Chapter 20. Escherichia, 361.