Last to update on June 23rd, 2021Mannitol salt agar (MSA) is a selective, differential, and also indicator tool that is provided to isolate and identify Staphylococcus aureus from the clinical specimen. As its name argues mannitol salt agar (MSA) includes 1% mannitol (sugar), 7.5% salt, and agar together a solidifying agent. Members the the genus Staphylococcus can tolerate high salt concentration (7.5%) and also grow ~ above mannitol salt agar.

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Growth the S. Aureus and CONS ~ above MSA (Image source: Pearson Education)
Shelf life: several weeks giving there is no readjust in the illustration of the medium to suggest contamination, deterioration, or alteration of pH.pH the medium: This must be in ~ the selection of pH 7.3 to 7.7 at room temperature.Staphylococcus saprophyticus (coagulse-negative Staphylococci) may ferment mannitol, creating yellow halo roughly colonies in MSA hence resembling S. Aureus.Colony attributes in Mannitol Salt AgarEscherichia coli: Does not growStaphylococcus epidermidis: Colorless to pink coloniesStaphylococcus aureus: Yellow colonies; may have actually a yellow halo around colonies.Note: carry out not do coagulase test from the colonies isolated native mannitol salt agar.

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Troubleshooting: When get an impression on mannitol salt agar some varieties of Micrococcus (Micrococcus is a normal flora of human being skin, mucosa, and oropharynx), such as M. Luteus (yellow) can create yellow colonies. M. Roseus (red) to produce pink swarms on MSA. Uncover out difference in between Micrococcus and also Staphylococcus hereEnterococcus faecalis and also Enterococcus faecium (the most typical enterococcal varieties that has been isolated from person infections) are salt-tolerant bacteria. They can ferment mannitol and also produce lactic acid, developing yellow-colored nests on MSA. Catalase test can assist to differentiate between Enterococcus (-ve) and also Staphylococcus (+ve).