What makes mannitol salt agar differential

With my respect. If the organism in MSA ferments mannitol and forms yellow colonies, can we directly assume it as S. What is the ideal method? Please explain this. If you find the MSA turned yellow, S. Aureus is there, but it is regarded as presumptive test; one should perform coagulase test too.

Streak on NA to adopt pure culture and then perform coagulase test. Save my name and email in this browser for the next time I comment. Principle of Mannitol Salt Agar Mannitol Salt Agar contains peptones and beef extract, which supply nitrogen, vitamins, minerals and amino acids essential for growth. Uses of Mannitol Salt Agar It is used for the selective isolation and differentiation of Staphylococcus aureus from clinical samples. It is also used for the enumeration of staphylococci in food and dairy products.

This medium is also included in the Bacteriological Analytical Manual for cosmetics testing. It is also used in the bacteriological examination of swimming pool water, spas and drinking water using membrane filtration Preparation of Mannitol Salt Agar Suspend Boil to dissolve the media completely. Staphylococci other than S. Staphylococcus epidermidis Colorless or Red colonies with red zones. Streptococci No growth to trace growth. Micrococci Large white to orange.

Gram-negative bacteria No growth to trace growth. Limitations of Mannitol Salt Agar Several Staphylococcus species other than aureus are mannitol positive and produce yellow colonies surrounded by yellow zones on this medium e. Therefore, further biochemical tests are necessary for the identification of S. Most organisms other than staphylococci are inhibited by the high salt concentration found in Mannitol Salt Agar except for some halophillic marine organisms. A few strains of Staphylococcus aureus may exhibit a delayed fermentation of mannitol.

Negative plates should be re-incubated overnight before discarding. Presumptive Staphylococcus aureus must be confirmed with a coagulase test. This concentration inhibits the growth of most other gram-positive and gram-negative bacteria. Thus MSA selectively isolates Staphylococcus spp i. Pathogenic staphylococci, i. Staphylococcus aureus is able to ferment mannitol but others coagulase-negative staphylococci are not.

So, if that particular specimen contains S. 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.

Remember that in the neutral pH 6. You can purchase prepared mannitol salt agar from commercial suppliers or get the powder and prepare the media in your laboratory. Mannitol salt agar is best prepared from ready-to-use dehydrated powder, available from most suppliers of culture media. The medium is usually used at a concentration of Shelf life: Several weeks providing there is no change in the appearance of the medium to suggest contamination, deterioration, or alteration of pH.

Staphylococcus saprophyticus coagulse-negative Staphylococc i may ferment mannitol, producing yellow halo around colonies in MSA thus resembling S. Note: Do not perform coagulase test from the colonies isolated from mannitol salt agar.