Selective, differential medium for isolation of Salmonella and Shigella from clinical materials.
Hektoen Enteric Agar is a differential agar medium used for the isolation and identification of pathogenic Enterobacteriaceae from clinical specimens. The medium was developed for the isolation of Shigella sp. However, Salmonella sp. may also be isolated and identified using this medium. Bile salts are used in this medium to inhibit the growth of Gram positive bacteria. The inhibitory action of this medium has been tempered by increasing the concentration of peptones and carbohydrates and thus allowing better recovery and growth of Salmonella and Shigella sp. Bromthymol blue and acid fuchsin are used as acid-base indicators in this medium. Enteric bacteria which utilize lactose, sucrose or salicin with acid production give yellow-orange to salmon colored colonies. Salmonella and Shigella colonies are green to bluish green in color. Hydrogen sulfide producing bacteria, such as Salmonella, will produce black centered colonies in the presence of ferric ammonium citrate and sodium thiosulfate.
Appearance:Beige with green tint, homogeneous, free flowing powder
Solubility:Light to dark green, clear to trace hazy
pH (7.5% @25ºC):7.6 ± 0.2
Microorganisms:Enterobacter aerogenes ATCC 13048Growth/yellow to salmon colored colonies with bile precipitateEscherichia coli ATCC 25922InhibitedProteus vulgaris ATCC 13315InhibitedSalmonella typhimurium ATCC 14028Growth/green w/black centersShigella flexneri ATCC 12022Growth/blue-green colonies
