Hektoen Enteric Medium

Hektoen Enteric (HE) Agar is a moderately selective medium used in qualitative procedures for the isolation and cultivation of gram-negative enteric microorganisms, especially Shigella and Salmonella from a variety of clinical and nonclinical specimens. King and Metzger developed this medium from the previously formulated Salmonella-Shigella (SS) Agar1 which contains synthetic detergent which is inhibitory to Gram-positive bacteria and many Gram- negative bacteria. The formulation incorporates larger amounts of peptone in order to offset the inhibitory effect of bile salts. Lactose present in the medium makes helps to differentiate lactose fermenters from non- lactose fermenters like Salmonella and late-lactose fermenters like Shigella, and bile salts inhibits gram-positive organisms.

Coliforms capable of overcoming the moderately inhibitory effect of the medium will develop into orange or salmon-pink colonies in the presence of the bromthymol blue indicator. Shigella species develop into green-colored colonies with darker blue-green centers. Salmonella species appear as blue-green colonies with or without black centers. The addition of ferric ammonium citrate and sodium thiosulfate enable the detection of H2S, noted by the production of black centered colonies. The H2S producing coliforms like Proteus and Salmonella grow in the medium forming clear colony with a black center. Sodium thiosulfate serves as the sulfur source while ferric ammonium citrate serves as the indicator.

Product NameCatalog #Quantity
Hektoen Enteric Agar mono plate, 90 x 15 mm CH9370P 10/pk
Hektoen Enteric Slant CH9370S 10/pk
Hektoen Enteric Broth CH9370B 20/pk

Quality Control

The following organisms are routinely used for testing for this medium.
Test OrganismsResults
Salmonella enterica ATCC® 14028 Growth; blue to blue-green colonies with black centers
Shigella flexneri ATCC® 12022 Growth; green to blue-green colonies
Enterococcus faecalis ATCC® 29212 Inhibition; may be slight growth of yellow colonies
Escherichia coli ATCC® 25922 Partial inhibition; may be slight growth of yellow to salmon colored colonies

User Quality Control

Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 7.6 +/- 0.2 at 25°C)
Peptic Digest of Animal Tissue 12.0
Lactose 12.0
Sucrose 12.0
Bile Salts 9.0
Sodium Chloride 5.0
Sodium Thiosulfate 5.0
Yeast Extract 3.0
Salicin 2.0
Ferric Ammonium Citrate 1.5
Acid Fuchsin 0.1
Bromothymol Blue 0.064
Agar 13.5
1 total citations

  1. King, S., and Metzger, W.I. 1968. Applied Microbiology; 16:577-579.
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