Biochemical Tests for Bacterial Identification

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

Last updated on June 21st, 2021

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

Beta-glucuronidase test (MUG Test)

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

Bacitracin Sensitivity Test

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

Bile solubility test

To differentiate Streptococcus pneumoniae from other alpha hemolytic streptococci. Bile or a solution of a bile salt, such as sodium desoxycholate rapidly lyses pneumococcal colonies.

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

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.

Catalase test

To differentiate Staphylococci (catalase-positive) from Streptococci (catalase test negative)

Citrate utilization test

To differentiate members of Enterobacteriaceae family.

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.

DNase test

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

Indole test

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

Litmus milk decolorization test

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

Lysine Decarboxylase test

To assist in the identification of Salmonella and Shigella

Oxidase test

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

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.

About Acharya Tankeshwar 473 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.