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