3.12.1: Mannitol Salt Agar Test

OER - BIOL 2420 Laboratory Manual · LibreTexts

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    The mannitol salt agar is also a selective and differential media. This media contains 7.5% NaCl, which creates an environment on which only salt tolerant (facultative halophiles) can grow. This concentration of salt selects for organisms within the Staphylococcus genera, because most other bacteria cannot survive such high concentrations of salt. The media also contains the sugar mannitol and the pH indicator phenol red. These ingredients allow the microbiologists to differentiate between members of the Staphylococcus genus who are capable of fermenting mannitol and those who cannot. Pathogenic species of Staphylococci are capable of mannitol fermentation, whereas non-pathogenic species grow on the mannitol salt agar but do not ferment the mannitol.

    Mannitol Salt Agar Results
    Positive Mannitol Fermenting Bacteria Non-Mannitol Fermenting Bacteria
    Examples:

    Staphylococcus aureus

    Staphylococcus haemolyticus    		 Examples:

    Staphylococcus epidermidis
    Mannitol salt agar: A, S. epidermidis nonfermenter; B, S. aureus fermenter; C, E. coli no growth.
    Mannitol salt agar. A) Staphylococcus epidermidis - facultative halophile, negative for mannitol fermentation B) Staphylococcus aureus - facultative halophile, positive for mannitol fermentation C) No growth - Escherichia coli failed to grow - unable to tolerate salt concentration. Credit: Sherry Smith

    This page titled 3.12.1: Mannitol Salt Agar Test was last modified on Sat, 25 Jul 2026 03:43:07 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Sherry Smith.