Why is mannitol salt agar selective for Staphylococcus aureus?
Welcome to Microbugz – Mannitol Salt Agar. Mannitol Salt Agar (MSA) is a selective and differential medium. The high concentration of salt (7.5%) selects for members of the genus Staphylococcus, since they can tolerate high saline levels. Organisms from other genera may grow, but they typically grow very weakly.
Is Staphylococcus aureus mannitol positive?
aureus are positive for mannitol and produce yellow colonies surrounded by yellow areas (eg S.
Does Staphylococcus Grow on mannitol salt agar?
Mannitol Salt Agar (MSA) This is a medium that is both selective and differential. The high salt concentration (7.5%) is the selective ingredient. Staphylococcus species, which commonly inhabit human skin, can grow on this high salt concentration (left plate in picture below).
How do Staphylococcus aureus bacteria appear on MSA agar?
Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium. If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow.
What is the purpose of the mannitol salt agar test?
Mannitol Salt Agar is used as a selective media for the isolation of pathogenic Staphylococci. It is recommended for the detection and enumeration of coagulase-positive Staphylococci in milk, food and other specimens. It is recommended in U.S.P. for use in the performance of microbial limit tests.
What type of bacteria grows on mannitol salt agar?
Mannitol is the fermentable carbohydrate source, fermentation of which leads to acid production. Staphylococcus aureus grows on this medium and ferments mannitol to produce yellow colonies. Most coagulase-negative species of Staphylococci and Micrococci do not ferment mannitol and grow as small red colonies.
What bacteria grows on mannitol salt agar?
Staphylococcus aureus and Staphylococcus epidermidis on mannitol salt agar. Mannitol salt agar is a commonly used growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others.
What grows on mannitol salt agar?
Staphylococcus aureus grows on this medium and ferments mannitol to produce yellow colonies. Most coagulase-negative species of Staphylococci and Micrococci do not ferment mannitol and grow as small red colonies.
What is in mannitol salt agar?
Mannitol Salt Agar contains beef extract and proteose peptone, which makes it very nutritious as they provide essential growth factors and trace nutrients. Many other bacteria except Staphylococci are inhibited by 7.5% sodium chloride. Mannitol is the fermentable carbohydrate source.
What does a positive mannitol test mean?
A positive test consists of a color change from red to yellow, indicating a pH change to acidic.
What agar does Staphylococcus epidermidis grow on?
Staphylococcus epidermidis grows on MSA, but does not ferment mannitol (media remains light pink in color, colonies are colorless). Fig. 8 Staphylococcus epidermidis on Mannitol Salt Agar.