Biochemical Test of Escherichia coli (E. coli)

Biochemical Test of Escherichia coli (E. coli)

Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacteria that lives in the intestines of humans and other warm-blooded animals. Biochemical tests are performed to identify bacteria based on their enzymatic and metabolic properties. These tests assist identify and differentiate Escherichia coli (E. coli), a common bacterium found in the intestines of humans and other animals. Biochemical tests are essential for identifying and differentiating bacterial species, including Escherichia coli (E. coli)

What is Escherichia coli (E. coli)?

Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacteria that lives in the intestines of humans and other warm-blooded animals. While most E. coli strains are innocuous and play an important role in intestinal health, others can cause serious food poisoning and other disorders.

Escherichia coli (E. coli

Here’s a detailed look at the biochemical assays used to detect Escherichia coli (E. coli):

1. Indole Test

Principle:

The indole test detects how the enzyme tryptophanase produces indole from the amino acid tryptophan. Indole is formed when tryptophan is hydrolyzed and can be identified using Kovac’s reagent.

Procedure:

To inoculate a tryptone broth, add the bacterial sample.
Incubate at 37°C for 24 to 48 hours.
Add a few of drops of Kovac’s reagent to the culture.

Expected Results:

Positive: A red ring appears on top of the medium, suggesting indole production.
Negative: There is no color shift; the color remains yellow or clear.

Significance:

This test distinguishes E. coli from other intestinal bacteria that do not produce indole.

2. Methyl Red (MR) Test

Methyl Red (MR) Test

Principle:

The MR test determines if bacteria produce stable acids from glucose fermentation, lowering the pH of the medium.

Procedure:

To proceed, inoculate the bacterial sample into MR-VP broth.
Incubate for 48 hours at 37 °C.
Apply a few drops of methyl red indicator.

Expected outcomes:

Positive: The medium turns red, indicating that the pH has dropped below 4.4 due to stable acid production.
Negative: The medium becomes yellow, suggesting a pH greater than 6.0.

Significance:

E. coli commonly ferments mixed acids, leading to a positive MR test.

3. Voges-Proskauer (VP) Test

 Voges-Proskauer (VP) Test

Principle:

The VP test identifies the neutral end product of glucose fermentation, acetoin, which is transformed to diacetyl in the presence of alpha-naphthol and potassium hydroxide.

Procedure:

Inoculate MR-VP broth with bacterial sample.
Incubate at 37 °C for 48 hours.
Combine VP Reagent A (α-naphthol) and VP Reagent B (KOH).

Expected Results:

Positive: A red hue appears within 15-30 minutes, indicating acetoin production.
Negative: No color change or a coppery brown tint.

Significance:

E. coli often results in a negative VP test because it does not produce acetoin.

4. Citrate Utilization Test

Principle:

The citrate utilization test checks if bacteria can use citrate as their sole carbon source. Citrate use causes an alkaline reaction because it produces ammonia.

Procedure:

To inoculate the Simmons citrate agar slant, add the bacterial sample.
Incubate at 37 °C for 48 hours.

Expected Results:

Positive: The media becomes blue, indicating citrate usage and an alkaline pH.
Negative: The medium remains green, indicating no citrate consumption.

Significance:

E. coli typically produces a negative result, indicating that it cannot use citrate as a sole carbon source.

5. Urease Test

Principle:

The urease test identifies the enzyme urease, which breaks down urea into ammonia and carbon dioxide, raising the pH of the medium.

Procedure:

Inoculate urea broth or agar with the bacterial sample.
Incubate at 37 °C for 24-48 hours.

Expected result:

Positive: The medium changes color to pink or crimson, suggesting a pH rise.
Negative: The medium stays yellow or unchanging.

Significance:

E. coli produces no urease, resulting in a negative urease test.

Frequently Asked Question(FAQ)

What is Escherichia coli (E. coli)?

Biochemical tests are performed to identify bacteria based on their enzymatic and metabolic properties. These tests assist identify and differentiate Escherichia coli (E. coli), a common bacterium found in the intestines of humans and other animals. Biochemical tests are essential for identifying and differentiating bacterial species, including Escherichia coli (E. coli)

What are the test of Escherichia coli (E. coli)?

The test of Escherichia coli (E. coli) are:
1. Indole Test
2. Methyl Red (MR) Test
3. Voges-Proskauer (VP) Test
4. Citrate Utilization Test
5. Urease Test

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Biochemical Test of Enterococcus faecalis