Hektoen Agar Plate Tests:

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This agar was formulated to help isolate enteric pathogens.   Hektoen Enteric Agar is used to isolate and differentiate Salmonella and especially Shigella from the other Gram negative enteric pathogens in clinical samples.

Hektoen agar is an undefined medium with yeast extract and peptone.   A high concentration of bile salts inhibits all Gram positives and some Gram negatives, but not Salmonella and Shigella.  Lactose, Sucrose, and Salicin plus the dyes bromthymol blue and acid fuchsin allow differentiation between  enterics due to to the colony and medium colors produced.  Coliforms produce yellow to salmon colonies.   Salmonella produces blue-green colonies and Shigella produces raised green moist colonies.  Black areas indicate hydrogen sulfide production.