Malonate test: Principle, Requirements, Procedure, and Result interpretations

Malonate test is a valuable tool in microbiology for differentiating bacteria based on their ability to utilize malonate as a sole carbon source. By observing the color change in the medium, microbiologists can gain insights into the metabolic capabilities of the bacteria, aiding in their identification and characterization.

Malonate test

A biochemical test called the malonate test is used to distinguish between different types of bacteria according to how well they can use sodium malonate as their only carbon source. When it comes to distinguishing between members of the Enterobacteriaceae family, this test is quite helpful.

Malonate test is a biochemical assay used in microbiology to determine the ability of bacteria to utilize sodium malonate as their sole carbon source. It is particularly employed to differentiate members within the Enterobacteriaceae family based on their metabolic capabilities. The test principle relies on the presence of the enzyme malonate decarboxylase, which allows certain bacteria to degrade and use malonate, producing alkaline by-products that increase the pH of the medium

Principle

The capacity of some bacteria to use malonate as their only carbon source forms the basis of the malonate test’s theory. Growing in a medium containing sodium malonate causes bacteria that can use malonate to produce alkaline byproducts that raise the medium’s pH. The medium-incorporated pH indicator, bromothymol blue, changes colour to indicate the presence of this pH shift.

Malonate test is a biochemical assay used to determine the ability of bacteria to utilize sodium malonate as their sole carbon source. This test is particularly useful in the differentiation and identification of members within the Enterobacteriaceae family, such as Klebsiella, Escherichia, and Shigella.

Requirements

• Malonate broth: Contains sodium malonate as the sole carbon source, ammonium sulfate as the nitrogen source, and bromothymol blue as the pH indicator.
• Bacterial culture: The organism to be tested.
• Incubator: Set at 35-37°C.
• Sterile inoculating loop or needle.

Procedure

Vaccination

A tiny amount of the bacterial culture should be added to the malonate broth using a sterile inoculating loop or needle.

Embryology

For 24 to 48 hours, incubate the inoculation tube at 35 to 37°C..

Note:

Examine the broth’s colour after the incubation period.

Result Interpretations

Positive Result:

• Visual Appeal: The green broth turns blue in hue.
• Interpretation: Malonate is the only carbon source that the organism can use. As a result, alkaline byproducts are produced, raising pH levels and turning the bromothymol blue indicator blue.

Negative Result:

• Visuals Appeal: The soup either stays green or becomes yellow.
• Meaning: The organism is unable to use malonate. Because other metabolic processes produce acidic by-products, the pH either stays neutral or becomes acidic, which determines whether the bromothymol blue indicator turns yellow or stays green.

Applications

• Enterobacteriaceae identification: The malonate test is especially helpful in distinguishing between species in this family. For instance, it aids in distinguishing Shigella and Escherichia (malonate-negative) from Klebsiella (malonate-positive).
• Clinical diagnostics: A method used in clinical labs to distinguish and identify bacterial infections.

Limitations

• Specificity: Although the malonate test has its uses, it should be used with other biochemical tests to verify the identification of bacteria because certain bacteria may provide unusual findings.
• Length of Incubation: For certain organisms to produce positive results, a longer incubation period may be necessary.

Frequently Asked Question

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