What does yellow mean on MSA plate?
Mannitol Salt Agar (MSA) is used to determine if the bacteria is halophilic (salt loving) and if the bacteria can ferment mannitol. A positive result for mannitol fermentation would be the formation of a yellow halo around the bacterial colony, this is an indication of acid production from the breakdown of mannitol.
What is a positive test for the mannitol salt agar?
In clinical samples, mannitol positive isolates are suggestive of Staphylococcus aureus and should be further tested. A non-fermenting bacteria that resists the high salt concentration results in a red to pink area due to the degradation of the peptone.
What color is MSA agar?
yellow
As MSA contains phenol red as a pH indicator, at pH levels below 6.9, the medium is a yellow color. But if coagulase-negative staphylococci (CONS) grows, they cant ferment mannitol, so the color of the media around the bacterial colony does not change to yellow, it appears pink. So, MSA is also a differential medium.
How does the yellowing of the medium happens when S aureus is inoculated in MSA?
MSA also contains the sugar mannitol and the pH indicator phenol red. If an organism can ferment mannitol, an acidic byproduct is formed that will cause the phenol red in the agar to turn yellow. The Staphylococcus aureus ferments mannitol and turns the medium yellow.
What color is the MSA pH indicator in a basic solution?
pH indicator: Phenol red Yellow colonies of S. aureus in Mannitol Salt Agar (MSA).
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.
What is the Colour of S aureus?
aureus is an aerobic and facultative anaerobic organism that forms fairly large yellow or white colonies on nutrient rich agar media. The yellow colour of the colonies is imparted by carotenoids produced by the organism. The term ‘aureus’ is derived from Latin, which refers to the colour of gold [5].
Why does Mannitol Salt Agar turn yellow?
What is the pH of mannitol salt agar?
7.4
pH 7.4 ± 0.2 at 25 °C.
Why is staph aureus yellow?
The golden color of Staphylococcus aureus is due to the synthesis of carotenoid pigments. In Gram-negative bacteria, Hfq is a global posttranscriptional regulator, but its function in S. aureus remains obscure.
Which of the following is responsible for the yellow pigment of Staphylococcus aureus?
Staphyloxanthin is a carotenoid pigment that is produced by some strains of Staphylococcus aureus, and is responsible for the characteristic golden color that gives S. aureus its species name. Staphyloxanthin also acts as a virulence factor.
Why is phenol red in MSA agar?
MSA also contains the sugar mannitol and the pH indicator phenol red. If an organism can ferment mannitol, an acidic byproduct is formed that will cause the phenol red in the agar to turn yellow. Most pathogenic staphylococci, such as Staphylococcus aureus, will ferment mannitol.
Why is MSA agar selective as well as differential?
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. Also, why is MacConkey agar selective as well as differential?
Why is MSA media yellow in color?
So, if that particular specimen contains S. aureus, it ferments mannitol (whenever sugar is fermented acid is produced) and changes the pH of medium to acidic. As MSA contains phenol red as a pH indicator, at pH levels below 6.9, the medium is a yellow color.
Why does red mannitol turn yellow in MSA?
MSA also contains the sugar mannitol and the pH indicator phenol red. If an organism can ferment mannitol, an acidic byproduct is formed that will cause the phenol red in the agar to turn yellow.