Various dyes, pH indicators, and other ingredients are included in differential plating media to serve as indicators of enzymatic activities and aid in identifying bacterial isolates.
For example in MacConkey agar, lactose fermenting colonies appear pink and lactose nonfermenting colonies appear pale or clear whereas the lactose fermenting colonies appear yellow in Hektoen-Enteric agar. This is because of the production of acids and subsequent changes in pH. As different pH indicators are used in these media, the colors of the colonies are different.
Tinsdale Agar is used for the selective isolation and differentiation of C. diphtheriae from diphtheroids.
Deoxycholate citrate agar is used for the selective isolation and differentiation of Salmonella and Shigella species.
Bismuth sulfite agar is a modification of original Wilson and Blair medium used for the isolation of Salmonella typhi and other salmonellae.
It contain chromogenic substrate which is utilized by the microorganisms to give colored colonies that is specific for each microorganism.
Salmonella-shigella (SS) agar is commonly used for the selective isolation and differentiation of Salmonella and Shigella.
Differential medium used for urine culture as it inhibits the swarming of Proteus and also supports the growth of gram-positive cocci.
Hektoen Enteric Agar (HE) is a selective and differential medium to isolate and differentiate Salmonella and Shigella from other Enterobacteriaceae.
TCBS agar is a selective as well as differential culture medium used for selective isolation and differentiation of Vibrio species.
Eosin methylene blue (EMB) agar is a selective and differential medium used to isolate fecal coliforms.
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.