Cultural Characteristics of E. coli
1. E. coli is facultative anaerobes.
2. Its optimum growth temperature is 37°C and ranges from 10°C to 40°C.
E. coli on Nutrient Agar (NA)
1. They appear large, circular, low convex, grayish, white, moist, smooth and opaque.
2. They are of 2 forms: Smooth (S) form and Rough (R) form.
3. Smooth forms are emulsifiable in saline.
4. Due to repeated sub culture, there is smooth to rough variation (S-R variation).
E. coli on Blood Agar (BA)
1. Colonies are big, circular, gray and moist.
2. Beta (β) hemolytic colonies are formed.
E. coli on MacConkey Agar (MAC)
1. Colonies are circular, moist, smooth and of entire margin.
2. Colonies appear flat and pink.
3. They are lactose fermenting colonies.
E. coli on Mueller Hinton Agar (MHA)
1. Colonies are pale straw colored.
E. coli on Eosin Methylene Blue (EMB) Agar
1. Green Metallic sheen colonies are formed.
E. coli on m-ENDO Agar
1. Colonies are green metallic sheen.
2. Metabolise lactose with the production of aldehyde and acid.
E. coli on Violet Red Bile Agar (VRBA)
1. Red colonies (pink to red) are formed.
2. Bluish fluorescence around are seen around colonies under UV.
E. coli on Cystine Lactose Electrolyte-Deficient (CLED) Agar
1. They give lactose positive yellow colonies.
E. coli on Liquid Media
1. They show homogenous turbid growth within 12-18 hours.
2. R form agglutinate spontaneously, forming a sediment on the bottom of the test tubes.
3. After prolonged incubation (>72 hrs), pellicle are formed on the surface of liquid media.
4. Heavy deposits are formed which disperses on shaking.