How does Staphylococcus aureus appear on MSA?

Staphylococcus aureus produce yellow colonies with yellow zones, whereas other 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 will cause the phenol red in the agar to turn yellow.

Does Staphylococcus aureus grow on MSA?

Mannitol Salt Agar is differential due to the presence of mannitol and the pH indicator Phenol Red. aureus grow on Mannitol Salt Agar. About 8 % to 12 % of Staph. aureus strains will not ferment mannitol.

What color is Staphylococcus aureus on MSA?

yellow
On MSA, pathogenic Staphylococcus aureus ferments mannitol, thereby changing the colour of the medium from red to yellow.

What does MSA agar test for?

Staphylococcus aureus
Uses of Mannitol Salt Agar (MSA) It is used for the selective isolation and differentiation of Staphylococcus aureus from clinical samples. It is also used for the enumeration of staphylococci in food and dairy products. This medium is also included in the Bacteriological Analytical Manual for cosmetics testing.

What Agar does Staphylococcus aureus grow on?

Staph. aureus will grow on general culture media such as Blood Agar and chocolated Blood Agar and therefore can be isolated from direct plating of clinical specimens. More specialised media, such as Staph/Strep Selective Medium contain antimicrobials.

What bacteria grows on MSA?

Result Interpretation on Mannitol Salt Agar

Organisms	Results
Staphylococcus aureus	Yellow colonies with yellow zones.
Staphylococci other than S. aureus (e.g. Staphylococcus epidermidis )	Colorless or Red colonies with red zones.
Streptococci	No growth to trace growth.
Micrococci	Large white to orange.

What organisms are inhibited from growing on MSA?

It contains a high concentration (about 7.5–10%) of salt (NaCl) which is inhibitory to most bacteria – making MSA selective against most Gram-negative and selective for some Gram-positive bacteria (Staphylococcus, Enterococcus and Micrococcaceae) that tolerate high salt concentrations.

What can grow on MSA plate?

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.

Can Streptococcus grow on MSA?

Mannitol Salt Agar (MSA) Staphylococcus species, which commonly inhabit human skin, can grow on this high salt concentration (left plate in picture below). This is in contrast to Streptococcus species, whose growth is selected against by this high salt agar (plate on the right in the picture below).

Why does mannitol salt agar turn yellow?

The differential ingredient in MSA is the sugar mannitol. Organisms capable of using mannitol as a food source will produce acidic byproducts of fermentation that will lower the pH of the media. The acidity of the media will cause the pH indicator, phenol red, to turn yellow.

Can E coli grow on MSA plate?

Gram-negative bacteria like E. coli and P. aeriginosa are not tolerant to salt (not halophilic) and will not grow colonies on MSA (see quadrants II and IV). Staphylococcus aureus is also able to ferment mannitol, because this bacterial species has the enzyme coagulase required for the process.