3.8.1: Casease Test

OER - BIOL 2420 Laboratory Manual · LibreTexts

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    From LibreTexts, under CC BY 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    The purpose of the casease test is to determine if a bacterium can hydrolyze the milk protein casein. Casein is a protein found in milk that is responsible for giving milk its white or cloudy appearance.

    Some bacteria can produce the enzyme casease, which is used to catabolize the protein into smaller peptides that can then be taken up by the cell and used for the cell’s metabolism. This test is performed by inoculating the bacteria onto a skim milk agar. If the bacteria have the enzyme casease, they will hydrolyze the casein causing the area around the bacteria to become clear.

    Casein Hydrolysis Results
    Positive Casein Hydrolysis Results Negative Casein Hydrolysis Results
    Examples:

    Bacillus subtilis

    Bacillus cereus    		 Examples:

    Escherichia coli

    Acinetobacter baumannii

    Salmonella enterica
    Casease test: side A shows casein hydrolysis; side B shows no casein hydrolysis.
    Casease Test - This digitally enhanced photo is the combined results of bacteria that are able to externally hydrolyze the milk protein, casein (side A), and bacteria that are unable to hydrolyze casein (side B). Source: Eunice Laurent, Wikimedia Commons, CC BY 4.0

    This page titled 3.8.1: Casease Test was last modified on Sat, 25 Jul 2026 03:43:02 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Sherry Smith.