Baird parker agar

Specifications

Ingredients : gms/lit.
Tryptone 10.00
Beef extract 5.00
Yeast extract 1.00
Glycine 12.00
Sodium pyruvate 10.00
Lithium chloride 5.00
Agar 20.00
Final pH (at 25°C) : 7.0 + 0.2

Directions :
Suspend 63.0 grams in 950 ml distilled water. Heat to boiling to dissolve the medium completely.
Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 50°C and aseptically add
50 ml concentrated Egg Yolk Emulsion (BF003) and 3 ml sterile 3.5% Potassium Tellurite solution
(BF008) or 50 ml Egg Yolk Tellurite Emulsion (BF007). Mix well and pour into sterile petri plates.

Principle :
Tryptone, Beef extract and yeast extract are sources of nitrogen, carbon, sulphur and vitamins.
Sodium pyruvate not only protects injured cells and helps recovery but also stimulates Staphylococcus
aureus growth without destroying selectivity. Lithium chloride and potassium tellurite inhibit most of
the contaminating microflora except Staphylococcus aureus. The tellurite additive is toxic to egg yolkclearing
strains other than S.aureus and imparts a black colour to the colonies. With the addition of
egg yolk, the medium becomes yellow, opaque. Proteolytic bacteria produce a clear zone around
colony in egg yolk containing media. A clear zone and grey-black colonies on this medium are
diagnostic for coagulase positive Staphylococci. Upon further incubation, an opaque zone is developed
around colonies which can be due to lipolytic activity.