Food microbiology — Colonies of <em>Staphylococcus aureus</em> grown on Baird–Parker agar are typically associated with which confirmatory property?

Introduction / Context:
Baird–Parker agar is a selective–differential medium commonly used to isolate presumptive Staphylococcus aureus from foods. It contains tellurite and egg yolk; S. aureus typically forms black, shiny colonies due to tellurite reduction, often with clear zones from lipolytic/lecithinase activity. However, laboratory identification requires a confirmatory test associated with this species: the coagulase test.

Given Data / Assumptions:

• We are dealing with “suspected” colonies on Baird–Parker medium.
• Final confirmation relies on biochemical properties characteristic of S. aureus.

Concept / Approach:
Most clinically and food-borne significant S. aureus strains are coagulase-positive, differentiating them from many coagulase-negative staphylococci. While catalase is positive in all staphylococci (and thus non-discriminatory), and protease activity is not a standard confirmatory trait, coagulase is the classical confirmatory test paired with Baird–Parker isolation.

Step-by-Step Solution:

Verification / Alternative check:
Food microbiology standards specify coagulase testing (and often latex agglutination for clumping factor/protein A) to confirm S. aureus from Baird–Parker plates.

Why Other Options Are Wrong:

• Protease activity: not a routine confirmatory hallmark for S. aureus.
• Catalase activity: shared by nearly all staphylococci; not specific.
• None of these: incorrect; coagulase is the classical confirmatory marker.

Common Pitfalls:
Assuming colony appearance alone is definitive; always run coagulase or equivalent confirmatory tests.

Final Answer:
coagulase activity