When using MSA plates what shows a positive result?

When using MSA plates what shows a positive result?

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 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 is the result of this coagulase test?

Principle of Coagulase Test This results in an alternation of fibrinogen so that it precipitates on the staphylococcal cell, causing the cells to clump when a bacterial suspension is mixed with plasma. This complex in turn reacts with fibrinogen to produce the fibrin clot.

Why does Staphylococcus aureus grow on mannitol salt agar?

Staphylococcus aureus produces small colonies surrounded by yellow zones. The reason for this change in color is that S. aureus ferments the mannitol, producing an acid, which changes the indicator from red to yellow. Those staphylococci that do not ferment mannitol show a purple or red zone around the colonies.

Is E coli MSA positive?

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). Pathogenic gram-positive Staphylococcus aureus salt-tolerant (halophilic) and will produce colonies on MSA.

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 is the function of coagulase?

Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of Staphylococcus isolates.

What is the coagulase test for?

Coagulase is an enzyme that clots blood plasma. This test is performed on Gram-positive, catalase positive species to identify the coagulase positive Staphylococcus aureus. Coagulase is a virulence factor of S. aureus.

Does Staphylococcus aureus grow on MacConkey Agar?

MacConkey agar selects for organisms like Escherichia coli (Gram negative bacilli) while inhibiting the growth of organisms like Staphylococcus aureus (Gram positive cocci). The plate on the right has Staphylococcus aureus growing and changes the color of the agar to yellow.

Can E. coli grow on MSA agar?

The MSA agar will retain its initial red color and will not change to yellow. 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).

What do you need to know about the slide coagulase test?

Coagulase is an enzyme produced by S. aureus that converts (soluble) fibrinogen in plasma to (insoluble) fibrin. Staphylococcus aureus produces two forms of coagulase, bound and free. Slide coagulase test is done to detect bound coagulase or clumping factor. Tube coagulase test is done to detect free coagulase.

How is MSA used for the isolation of Staphylococcus aureus?

Mannitol Salt Agar for the isolation of Staphylococcus aureus. Mannitol Salt Agar (MSA) is used as a selective and differential medium for the isolation and identification of Staphylococcus aureus from clinical and non-clinical specimens. It encourages the growth of a group of certain bacteria while inhibiting the growth of others.

What kind of coagulase test can be done on mannitol salt agar?

Note: Do not perform coagulase test from the colonies isolated from mannitol salt agar. When grown on mannitol salt agar some species of Micrococcus ( Micrococcus is a normal flora of human skin, mucosa, and oropharynx), such as M. luteus (yellow) can produce yellow colonies. M. roseus (red) produces pink colonies on MSA.

What’s the difference between MSA and phenol red?

So, MSA is also a differential medium. Remember that in the neutral pH (6.9 to 8.4) the color of phenol red is red; while above pH 8.4, the color of phenol red is pink. Other commonly used media that contain Phenol red as pH indicator are; TSI Agar, Urea base agar and XLD Agar.