This test is used as a screening tool for tuberculosis (TB) which is caused by a bacterium Mycobacterium tuberculosis.
Category: Biochemical Tests
Biochemical tests are the tests that are performed on different bacteria for their identification based on their biochemical activities towards different biochemical compounds.
- Biochemical tests are one of the traditional methods for the identification of microorganisms, generally performed with phenotypic identification.
- For many years, these methods were widely used and continue to be used today, especially in some laboratory routines where a particular type of microorganism must be quickly identified.
- The ability of microorganisms to utilize certain biomolecules, resulting in useful organic compounds on their own, forms the basis of various biochemical tests.
- Biochemical tests are of different types, where the identification or distinction between different microorganisms is carried out on various bases.
- One of the traditional methods commonly used is a simple visual detection of the growth of the organism in the presence of essential nutrients due to increased turbidity in the liquid medium.
- In other tests, however, the results are based on the color change of the medium as a result of the change in pH of the medium.
- Microorganisms can be classified into different groups based on their reaction to such tests. Some tests even allow the distinction of microorganisms at the species level.
- Biochemical tests are therefore essential as they are inexpensive and relatively simple to perform.
- The physiology of bacteria and other microorganisms differ from each other, which allows the differentiation of these microorganisms.
- However, biochemical tests have some drawbacks. Despite being inexpensive and allowing both quantitative and qualitative information on the diversity of microorganisms present in a sample, these methods are laborious and time-consuming and results are only seen after several days.
- In some cases, false positives are obtained, especially when considering similar microbial species.
A biuret test is a chemical assay that helps check for the presence of protein in a given sample. To confirm the presence of protein, it will rely on the changes in color.
Ninhydrin is a chemical that detects ammonia and amines (primary and secondary). Once ninhydrin reacts with these chemicals, it produces an intense blue or purple color: Ruhemann purple.
Citrate utilization can be used to distinguish between coliforms such as Enterobacter aerogenes (+ve) which occur naturally in the soil and in aquatic environments and fecal coliforms such as Escherichia coli (-ve) whose presence would be indicative of fecal contamination.
It is a procedure that helps determine the microorganism’s ability to produce acetylmethyl carbinol, which is a neutral reacting end product.
Methyl Red (MR) test is a biochemical test performed on bacterial species to detect the ability of an organism to produce stable acids end products (Mixed-acid fermentation) from supplied glucose.
Indole test is the a biochemical test performed on bacterial species to detect the ability of an organism to degrade the amino acid tryptophan and produce indole. It is used as the part of the IMViC tests, a set of four useful reactions that are commonly designed for the differentiation of enterics (members of family Enterobacteriaceae). The IMViC series includes following four tests Indole test Methyl red test Voges-Proskauer test Citrate test Principle of Indole Test Some […]
Urease test is a procedure used to find out the organism’s ability to split urea by producing an enzyme urease. Principle Decarboxylation of amino acids leads to the production of urea. Once urea undergoes hydrolysis, it produces ammonia and carbon dioxide. Urea is acidic but the formation of ammonia turns the medium into alkaline. The change in pH is indicated by the changes in color from light orange to magenta. Hence, an organism that tests […]
The oxidase test is used to identify bacteria that produce cytochrome c oxidase, an enzyme of the bacterial electron transport chain. When present, the cytochrome c oxidase oxidizes the reagent (tetramethyl-p-phenylenediamine) to (indophenols) purple color end product. When the enzyme is not present, the reagent remains reduced and is colorless. Purpose of Oxidase test Oxidase test is most helpful in screening colonies suspected of being one of the Enterobacteriaceae (all negative) and in identifying colonies suspected of belonging to other genera […]
Coagulase test is used to differentiate Staphylococcus aureus (positive) from Coagulase Negative Staphylococcus (CONS). Coagulase is an enzyme produced by S. aureus that converts (soluble) fibrinogen in plasma to (insoluble) fibrin. Staphylococcus aureus produces two forms of coagulase, bound and free. Slide coagulase test is done to detect bound coagulase or clumping factor. Tube coagulase test is done to detect free coagulase. Coagulation Test (Slide Method) Emulsify a staphylococcal colony in a drop of water […]