Which organism is classically described as catalase-positive, coagulase-positive, and capable of fermenting mannitol?

Which organism is classically described as catalase-positive, coagulase-positive, and capable of fermenting mannitol?

• A. Streptococcus pneumoniae
• B. Escherichia coli
• C. Staphylococcus aureus
• D. Enterococcus faecalis

Answer: (C)

The organism identified by this combination is Staphylococcus aureus. The first clue is catalase positivity, which distinguishes staphylococci (catalase-positive) from streptococci and enterococci (catalase-negative). The second clue is coagulase positivity, which sets apart S. aureus from other staphylococci that are coagulase-negative. The third clue is the ability to ferment mannitol, which on mannitol salt agar yields acid and turns the medium yellow, a trait characteristic of S. aureus. Taken together, catalase-positive, coagulase-positive, and mannitol fermentation points specifically to Staphylococcus aureus. The other organisms listed do not exhibit this exact combination: for example, streptococci are catalase-negative, enterococci are typically catalase-negative, and while some E. coli can ferment various sugars, the key differentiator here is coagulase positivity along with mannitol fermentation, which S. aureus uniquely shows among the options.

The organism identified by this combination is Staphylococcus aureus. The first clue is catalase positivity, which distinguishes staphylococci (catalase-positive) from streptococci and enterococci (catalase-negative). The second clue is coagulase positivity, which sets apart S. aureus from other staphylococci that are coagulase-negative. The third clue is the ability to ferment mannitol, which on mannitol salt agar yields acid and turns the medium yellow, a trait characteristic of S. aureus. Taken together, catalase-positive, coagulase-positive, and mannitol fermentation points specifically to Staphylococcus aureus. The other organisms listed do not exhibit this exact combination: for example, streptococci are catalase-negative, enterococci are typically catalase-negative, and while some E. coli can ferment various sugars, the key differentiator here is coagulase positivity along with mannitol fermentation, which S. aureus uniquely shows among the options.