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. Hektoen Enteric Agar is a differential agar medium used for the isolation and identification of pathogenic Enterobacteriaceae from clinical specimens. (Alpha Biosciences # H08-102-2Kg)
Use: Hektoen Enteric Agar is a differential agar medium used for the isolation and identification of pathogenic Enterobacteriaceae from clinical specimens.
Description: 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.
Formula* per Liter:
- Peptic Digest of Animal Tissue .... 12.0g
- Lactose ..........................................12.0g
- Yeast Extract .................................... 3.0g
- Bile Salts ......................................... 9.0g
- Sucrose .......................................... 12.0g
- Sodium Chloride............................. 5.0g
- Salicin ............................................... 2.0g
- Sodium Thiosulfate ........................ 5.0g
- Ferric Ammonium Sulfate ................1.5g
- Bromthymol Blue ....................... 0.065g
- Acid Fuchsin ..................................... 0.1g
- Agar .............................................. 13.5g
Final pH: 7.6 ± 0.2 at 25.0°C
* Grams per liter may be adj. or formula supplemented to obtain desired performance
Preparation: Mix 75 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. DO NOT AUTOCLAVE. Pour plates can be prepared after the medium has cooled to 45-50.0°C.
Quality Control Specifications:
- The powder is homogeneous, free flowing and light greenish-beige.
- Visually the prepared medium is clear to trace hazy and light to dark green in color.
- Expected cultural response after 18-24 hours at 35.0°C.
Organism                                                                                  Result
Enterobacter aerogenes ATCC 13048Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Growth/ yellow to salmon colored Â
                                                                                     colonies with bile ppt
Escherichia coli ATCC 25922Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Inhibited/ yellow-orange w/ bile ppt
Proteus vulgaris ATCC 13315Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Inhibited/ clear to yellowish
Salmonella typhimurium ATCC 14028Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Growth/ green w/ black centers
Shigella flexneri ATCC 12022Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Growth/ blue-green colonies
Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light greenish-beige color.
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