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Category: Biochemical Tests

Citrate Utilization Test

Citrate Utilization Test

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.

Indole Test

Indole Test

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

Urease Test

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 […]

Oxidase Test

Oxidase Test

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

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 […]

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