Staphylococcus aureus on Baird Parker agar plate
Baird Parker Agar is a selective medium for the isolation and presumptive identification of coagulase-positive staphylococci. Lithium chloride and potassium tellurite act as selective agents. Egg yolk is the substrate to detect lecithinase production and lipase activity. Staphylococci produce dark gray to black colonies due to tellurite reduction; staphylococci that produce lecithinase break down the egg yolk and cause clear zones around respective colonies. An opaque zone of precipitation may form due to lipase activity (S.aureus).