Which medium is used for isolation and identification of staphylococcal species due to high salt concentration and mannitol fermentation?

Which medium is used for isolation and identification of staphylococcal species due to high salt concentration and mannitol fermentation?

• A. Blood agar
• B. Chocolate agar
• C. Mannitol Salt Agar
• D. MacConkey agar

Answer: (C)

Mannitol Salt Agar uses high salt to selectively allow staphylococci to grow, since these bacteria tolerate the salty environment while many others cannot. It also contains mannitol and a pH indicator. If a staphylococcus ferments mannitol, acid is produced and the medium turns yellow around the colony, pointing to Staphylococcus aureus. If the organism does not ferment mannitol, the surrounding medium stays red, typical of other non-mannitol-fermenting staphylococci. This combination of selective growth and differential fermentation makes it ideal for isolating staphylococci and distinguishing S. aureus from other species. Other media lack this salt-based selectivity or the mannitol-differential component, so they’re not as appropriate for this purpose.