Baird Parker Agar Base ISO
Principles and uses
Bair Parker Agar Base is used for the isolation and enumeration of coagulase-positive staphylococci in food and other materials. Its formula is described in ISO 6888-1 normative.
Casein pancreatic digest, beef extract and yeast extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Lithium chloride, trypsin inhibitor and potassium tellurite inhibit the accompanying flora, and glycine and sodium pyruvate facilitate the staphylococci growth. Bacteriological agar is the solidifying agent.
The ISO 6888-1 Standard recommends adding Egg Yolk Tellurite Emulsion Supplement to Baird Parker Agar Base to make the complete medium Baird Parker Agar, used for the general count of coagulase-positive staphylococci in products intended for human or animal feed, through the
counting of colonies obtained in a solid medium. The identity of Staphylococcus aureus isolated on Baird Parker Agar must be confirmed with a coagulase reaction.
The ISO 6888-2 Standard recommends the addition of Rabbit Plasma Fibrinogen (RPF) Supplement to Baird-Parker Agar Base, to make Rabbit Plasma Fibrinogen (RPF) Agar used for food (such as cheese made from raw milk and certain raw meat products) that may be contaminated with: Staphylococcus forming non-characteristic colonies in Baird-Parker Agar or with base flora that can mask the colonies sought. This medium should be used immediately after preparation.
In Baird-Parker Agar the characteristic colonies are black or grey, shiny and convex and surrounded by a clear area. After 24 h of incubation an opalescent ring may appear in the clear area. Non characteristic colonies may be bright black or gray, with or without a narrow white border, without a clear area or opalescent ring.
In Rabbit Plasma Fibrinogen Agar, staphylococcus colonies are small, black or gray, even white, surrounded by a halo of precipitation indicating the coagulase activity. At the start of incubation, Proteus colonies can present similar physical characteristics to coagulase-positive Staphylococcus aureus colonies. However, after 24 or 48 hours of incubation, they can acquire a brown color that expands and invades the plate, and which allows them to be distinguished from staphylococcus.