About this test
What is the purpose of the test?
This test determines whether the microbe can grow on a nutrient medium where the concentration of sodium chloride (NaCl) is 7.5%.
How is growth on 7.5% NaCl determined?
If the microbe can grow in the presence of 7.5% NaCl , the broth will become turbid (cloudy) after incubation. If an agar plating medium is used, growth is indicated by appearance of bacterial colonies following incubation.
What medium is used?
For VirtualUnknown:Microbiology™, the medium used is mannitol salt agar . This is a nutrient medium with 7.5% sodium chloride (NaCl) added.
How is the test performed?
An inoculum from a pure culture is transferred aseptically to a sterile plate of mannitol salt agar and streaked for isolation across its surface. The inoculated plate is incubated at 35-37 C for 24 hours. A positive test is indicated by the presence of colonies on the streak marks placed on the agar surface.
What reagents are added?
None.
Performing this test in the VUMIE Online lab
1. Select the mannitol salt agar plate medium.
2. Using an inoculating loop, complete the process of a tube-to-plate aseptic transfer to inoculate the medium.
Incubation of the Inoculated Medium
3. Place the inoculated tube into the 35-37 C incubator.
4. Press the New Day button to move forward 24 hours.
Determination of Test Results
5. Incubate this test for only 24 hours.
6. Retrieve the incubated culture from the incubator.
7 . Observe the medium for the appearance of colonies in the plate. The culture producing colonies on the streak lines is capable of growing in the presence of 7.5% NaCl. NOTE: In some instances, the growth of the bacterium will have altered the color of the agar culture medium. The color of the medium is inconsequential to the positive result for growth in the presence of 7.5% NaCl. For information on the meaning of color changes when using this medium, refer to the information about the medium, mannitol salt agar , or to the mannitol fermentation test.
Uninoculated Mannitol Salt Agar plate
Positive for Growth on 7.5% NaCl and Positive for Mannitol Fermentation
Positive for Growth on 7.5% NaCl but Negative for Mannitol Fermentation
Negative for Growth on 7.5% NaCl