What does the change in color of the MSA medium indicate?

The NaCl inhibits organisms other than staphylococci. If the mannitol is fermented to produce acid, the phenol red in the medium changes color from red to yellow. it indicates that the organisms are salt tolerant. What does the gram stain help us do on the MSA and SM110 plates?

What does a positive look like on an 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 the indicator in MSA media?

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 does a positive MSA plate look like for Staphylococcus aureus?

Results. Yellow colonies with yellow zones. Colorless or Red colonies with red zones. No growth to trace growth.

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).

What are the roles of mannitol and phenol red 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. Most pathogenic staphylococci, such as Staphylococcus aureus, will ferment mannitol.

What is blood agar plate?

Blood agar is a general purpose, enriched medium often used to grow fastidious organisms and to differentiate bacteria based on their hemolytic properties. In the U.S., blood agar is usually prepared from tryptic soy agar or Columbia agar base with 5\% sheep blood.

What is phenol red indicator?

Phenol red, also known as phenolsulfonphthalein, is a pH indicator dye that exhibits a gradual transition from yellow to red over a pH range of 6.2 to 8.2 (Figure 2). Above 8.2 the dye turns a bright fuchsia color.

What color is the MSA pH indicator in acid?

Objectives: Mannitol Salt Agar (MSA) medium used to distinguish mannitol fermented ability among Staphylococcus species. The ability to ferment mannitol visualized by color changing in agar medium. Fenol red is color indicator usually used in standard MSA medium which has ability to turn from red to yellow in acid pH.

Is phenol red acidic or basic?

It is a weak acid with pKa = 8.00 at 20 °C (68 °F). A solution of phenol red is used as a pH indicator, often in cell culture. Its color exhibits a gradual transition from yellow (λmax = 443 nm) to red (λmax = 570 nm) over the pH range 6.8 to 8.2. Above pH 8.2, phenol red turns a bright pink (fuchsia) color.

What is the color of Escherichia coli on mannitol salt agar?

Red
Results on Mannitol Salt Agar (MSA)

Why do bacteria lyse red blood cells?

Function. A function of hemolysins is that the bacteria can utilize hemolysis to release and utilize nutrients from the host animal cells. Iron e.g., is essential to many pathogenic bacteria, but is only present in very low concentrations outside the cells.