Gram-positive bacteria retain the crystal violet-iodine complex and stain purple, whereas gram-negative bacteria stain pink.
Catalase test is used to distinguish among Gram-positive cocci. Staphylococci are catalase-positive but Streptococci are catalase-negative.
Blood agar is an enriched medium which supports growth of gram-positive cocci and differentiates them on the basis of hemolysis (α, β, or γ).
Selective (against gram-positive bacteria) and differential culture medium (LF and NLF), commonly used for the isolation of enterics.
TSI test determines whether a gram-negative rod utilizes glucose, and lactose or sucrose fermentatively and forms hydrogen sulfide.