What does an MSA plate test for?
Mannitol Salt Agar (MSA) is used to determine if the bacteria is halophilic (salt loving) and if the bacteria can ferment mannitol. If the bacteria is able to grow then it is a halophilic bacteria, due to it’s ability to grow in a high salt environment.
What is the MSA test in microbiology?
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.
Which bacteria is positive on MSA test?
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.
Can gram positive grow on MSA?
MSA also distinguishes bacteria based on the ability to ferment the sugar mannitol, the only carbohydrate in the medium. Staphylococci can withstand the osmotic pressure created by 7.5% NaCl, while this concentration will inhibit the growth of most other gram- positive and gram-negative bacteria (14).
What bacteria grows on MSA agar?
Results on Mannitol Salt Agar (MSA)
| Organisms | Results |
|---|---|
| Staphylococcus aureus | Yellow colonies surrounded by the yellow zone |
| Staphylococcus epidermidis | Pink or Red colonies |
| Micrococci | Red colonies |
| Escherichia coli | No growth |
Is Staphylococcus Saprophyticus mannitol positive?
Staphylococcus saprophyticus (coagulse-negative Staphylococci) may ferment mannitol, producing yellow halo around colonies in MSA thus resembling S. aureus.
Does gram negative bacteria grow MSA?
Selective medium Species of staphylococci are able to tolerate this salt concentration but other pathogenic bacteria may not. This concentration inhibits the growth of most other gram-positive and gram-negative bacteria. Thus MSA selectively isolates Staphylococcus spp i.e. selective media for Staphylococcus spp.
What is the selective agent in MSA?
Mannitol Salt Agar (MSA) contains mannitol (a sugar) and a high level of salt that limits the growth of many organisms. It is a clear pink colour and contains a pH inidcator that will turn yellow when acidic. In MSA, mannitol is. the selective agent.
Why is Mannitol Salt Agar used as a selective medium?
Mannitol salt agar (MSA) is both a selective and differential medium for culturing staphylococci which was originally described by Chapman (1945). The medium is selective because the presence of a high salt concentration (7ยท5%) suppresses the growth of most bacteria.
What can grow on MSA plates?
The MSA will select for organisms such as Staphylococcus species which can live in areas of high salt concentration (plate on the left in the 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 MSA plate turn yellow?
If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow.
Does Staphylococcus aureus grow on MSA?
Yes. It does not only support the growth of S. aureus but also makes it very easy to identify the organism on it especially because the agar supports the growth of other species of Staphylococcus species. This presence of this organism causes the red colour of the medium to change to yellow.
What grows on an MSA plate?
Why is MSA both selective and differential?
Mannitol Salt Agar (MSA) is both selective and differential. It contains 7.5% sodium chloride which selects for organisms that are halotolerant. It also contains the carbohydrate mannitol, and a pH indicator, phenol red, which allow distinction between organisms which can ferment mannitol and those that can not.
When a Mannitol Salt Agar plate turns yellow this indicates?
the agar plate is normally a red or pink color. turns yellow indicates that the bacteria ferements mannitol. would indicate that the bacteria is staphylococcus Aureus.
What bacteria grows on MSA plates?
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. |
How did the results observed on the mannitol salt agar?
How did the results observed on the mannitol salt agar and EMB agar correlate to the Gram reaction of the bacteria? Gram negative grows well on the EMB agar, gram positive grows well on the MSA.