Which bacterial species is often differentiated by its ability to ferment mannitol?

The ability to ferment mannitol is a key characteristic used to differentiate Staphylococcus aureus from other staphylococcal species. Staphylococcus aureus can ferment mannitol, leading to the production of acid, which in turn changes the color of the medium from red to yellow when using mannitol salt agar. This characteristic is utilized in laboratory diagnostics to help identify S. aureus in clinical specimens.

In contrast, while Staphylococcus saprophyticus and Staphylococcus epidermidis are both staphylococci, they do not display the same ability to ferment mannitol effectively, and thus, they typically do not cause the same color change in the medium. Streptococcus pyogenes, being a member of the Streptococcus genus, does not ferment mannitol and is unrelated to the characteristics assessed in mannitol fermentation tests that focus on staphylococci. The clear differentiation provided by this metabolic ability makes Staphylococcus aureus the correct choice for this question.