Hektoen Enteric (HE) Agar

Hektoen Enteric Agar is used for the isolation and differentiation of enteric pathogens. Hektoen Enteric Agar is not intended for use in the diagnosis of disease or other conditions in humans. Hektoen Enteric Agar was developed in 1967 by King and Metzger. Compared to other enteric differentiating media commonly used, Hektoen Enteric Agar increased the isolation rate of Salmonella spp. and Shigella spp. This was accomplished by increasing the carbohydrate and peptone content of the medium in order to counteract the inhibitory effects of bile salts and indicators. King and Metzger formulated a medium that slightly inhibited growth of Salmonella and Shigella, while inhibiting Gram-positive microorganisms. Enzymatic Digest of Animal Tissue provides nitrogen, carbon, and amino acids required for organism growth. Yeast Extract is a vitamin source. Bile Salts Mixture and Acid Fuchsin inhibit Gram-positive organisms. Lactose, Sucrose, and Salicin are fermentable carbohydrates. Sodium Chloride maintains the osmotic balance of the medium. Ferric Ammonium Citrate, a source of iron, allows the detection of hydrogen sulfide (H2S) produced from Sodium Thiosulfate. H2S-positive colonies have black centers. Bromothymol Blue is added as the pH indicator. Agar is the solidifying agent.