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;
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.
Bacitracin sensitivity test differentiates Streptococcus pyogenes (positive) from other beta hemolytic streptococci (resistant).
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.
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.
To differentiate Staphylococci (catalase-positive) from Streptococci (catalase test negative)
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.
This test is used to determine the ability of an organism to hydrolyze DNA. It is primarily used to identify Staphylococcus aureus.
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.
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.