Biochemical Tests for Bacterial Identification

In this blog post, I am sharing information about the standard, conventional biochemical tests and their primary uses in the Microbiology laboratory for identifying pathogens of interest. Some of the biochemical tests mentioned here, for example, catalase test, and oxidase test, assist us in many ways apart from the primary purpose mentioned in this post;

1. Beta-glucuronidase test (MUG Test)

MUG test is used to identify Escherichia coli. Escherichia coli produces the enzyme β-D-glucuronidase, which hydrolyzes β-D-glucopyranosid-uronic derivatives to aglycons and D-glucuronic acid.

Overview of Biochemical tests for differentiating Gram positive cocci
Overview of Biochemical tests for differentiating Gram positive cocci

2. Bacitracin Sensitivity Test

Bacitracin sensitivity test differentiates Streptococcus pyogenes (positive) from other beta-hemolytic streptococci (resistant).

3. Bile solubility test

Bile solubility test is used to differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci. Bile or a solution of bile salt, such as sodium desoxycholate rapidly lyses pneumococcal colonies.

CAMP test :
A. Streptococcus agalactiae (positive)
B. Streptococcus pyogenes (Negative)
Image Source: ASM

4. CAMP Test

Certain organisms such as Streptococcus agalactiae (Group B streptococci), produce a diffusible extracellular protein (CAMP) factor that acts synergistically with the beta-lysin of Staphylococcus aureus and causes enhanced lysis of RBCs.

5. Catalase test

Catalase test is used to differentiate Staphylococci (catalase-positive) from Streptococci (catalase test negative)

6. Citrate utilization test

To differentiate members of the Enterobacteriaceae family.

7. Coagulase test

Coagualse test is used to identify Staphylococcus aureus. Coagulase test differentiates Staphylococcus aureus (positive) from coagulase-negative staphylococci (CONS), such as S. epidermidis, S. saprophyticus.

8. DNase test

This test is used to determine the ability of an organism to hydrolyze DNA. It is primarily used to identify Staphylococcus aureus.

9. Indole test

This test is used to determine the ability of an organism to split tryptophan to form the compound indole. In a microbiology laboratory, it is used to differentiate gram-negative rods, particularly E. coli.

10. Litmus milk decolorization test

To help identify Enterococcus and some Clostridia, which have the ability to metabolize litmus milk.

11. Lysine Decarboxylase test

To assist in the identification of Salmonella and Shigella

12. Oxidase test

To help identify Neisseria, Pasteurella, Vibrio, and Pseudomonas. This test is used to determine the presence of bacterial cytochrome oxidase.

13. Urease test

Urease test is used to determine the ability of an organism to produce urease (an enzyme) that hydrolyzes urea. This test is done to help identify Proteus, Morganella, Yersinia enterocolitica, and Helicobacter pylori.

References and further reading

  1. Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson.
  2. Color Atlas and Textbook of Diagnostic Microbiology, Koneman, 5th edition

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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