E. coli: Introduction, Identification Features, Keynotes, and Escherichia coli Footages

Introduction of E. coli

Escherichia coli is a member of the family, Enterobacteriaceae and it is a Gram-negative, aerobe, and facultative anaerobic, rod-shaped bacterium. The optimal temperature for growth is 36-37°C with most strains growing over the range 18-44 °C. It is a commensal that is found inhabiting the lower intestine of our body. A small proportion of E. coli strains are pathogenic. 

The harmless strains produce vitamin K and prevent the colonization of the intestine by pathogenic bacteria. It is classified into serotypes based on cell wall (O), capsular (K), fimbria (F), and flagellar (H) antigens. e.g.  E. coli O157:H7

Pathogenic strains

1. Enterotoxigenic Escherichia coli (ETEC)
2. Enteropathogenic E.coli (EPEC )
3. Enteroinvasive E. coli (EIEC)
4. Enterohaemorrhagic E. coli (EHEC)
5. Enteroaggregative E. coli ((EAEC))

Identification Features of E. coli

Basic Features	Properties
1. Gram Staining	Gram-Negative Rods (GNRs)
2. Spore	Non-Sporing
3. Capsule	Capsulated (many isolates)
4. Motility	Motile
5. Pigment	Negative
6. Growth in potassium cyanide (KCN) medium	Negative
7. Catalase test	Positive
8. Oxidase test	Negative
9. Nitrate reduction test	Positive
10. MR (Methyl Red) test	Positive
11. VP (Voges- Proskauer) assay	Negative
12. OF (Oxidative-Fermentative) test	Fermentative
13. Gas from Glucose	Positive
14. H2S production	Negative
15. Indole formation	Positive
16. Urease/ urea hydrolysis test	Negative
17. Citrate/ citrate utilization	Negative
18. DNase test	Negative
19. Glucose fermentation	Positive
20. Maltose fermentation	Positive
21. Lactose fermentation	Positive
22. Sucrose fermentation	Negative
23. Xylose fermentation	Positive
24. Mannitol fermentation	Variable
25. Acetate Utilization	Positive
26. ONPG (β-galactosidase)	Positive
27. Phenylalanine Deaminase (PDA)/PPA Test	Negative
28. Lipase test	Negative
29. Esculin Hydrolysis test	Variable
30. Lysine Decarboxylase Test	Positive
31. Ornithine Decarboxylase Test	Variable
32. Arginine Dihydrolase Test	Negative

Escherichia coli Footages

Gram negative rods (GNRs) of Escherichia coli in Gram staining of culture

E. coli growth on MacConkey medium

E. coli colony morphology on blood agar

E. coli Colony Characteristics on Chocolate Agar

Indole positive Escherichia coli in MIU medium

Indole positive Escherichia coli in peptone water

Escherichia coli metallic green sheen on eosin methylene blue (EMB) agar demonstration

Sorbitol MacConkey Agar (SMAC) expressing sorbitol fermenting colony of Escherichia coli and the non-sorbitol fermenting colony of Escherichia coli

Escherichia coli on CLED agar

Further Readings

• https://www.sciencedirect.com/science/article/pii/B97801241584670000
• https://universe84a.com/sorbitol-macconkey-agar-smac-introduction/
• Cowan & Steel’s Manual for identification of Medical Bacteria. Editors: G.I. Barron & R.K. Felthani, 3rd ed 1993, Publisher Cambridge University Press.
• Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
• Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
• Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.