Baird-Parker Agar Base (Dehydrated) is a selective and sensitive medium specifically designed for the isolation and enumeration of Staphylococcus aureus, particularly from food samples.

This medium utilizes a carefully balanced blend of inhibitory agents—glycine, lithium, and tellurite—to suppress most background flora while allowing coagulase-positive staphylococci to thrive. The inclusion of egg yolk emulsion and sodium pyruvate is crucial for enhancing the recovery of stressed or damaged Staphylococcus aureus cells.

Key Features and Principles:

• Selective Isolation: Inhibitory agents prevent the growth of most non-target bacteria.
• Enhanced Recovery: Egg yolk and sodium pyruvate aid the recovery of damaged S. aureus cells.
• Clear Interpretation: Staphylococcus aureus colonies typically appear grey-black and shiny, surrounded by a clear zone due to proteolytic activity. Many strains also form an opaque halo upon further incubation.
• Diagnostic Indicators: The characteristic grey-black colony with a clear zone is highly indicative of S. aureus. However, colonies without an egg yolk reaction should be confirmed with a coagulase test, as some S. aureus strains, especially from cheese, may be egg yolk negative.
• Distinction from other Staphylococci: While some Staphylococcus saprophyticus strains may show similar reactions, they generally require longer incubation for zone formation.

Baird-Parker Agar Base is widely recognized and recommended by international bodies for its reliability in identifying Staphylococcus aureus.