Hektoen Enteric Agar

Use and description:   For the isolation and cultivation of Gram-negative enteric microorganisms (Salmonella and Shigella) from clinical specimens. Salicin, sucrose and lactose fermenting bacteria appear as yellow to orange colonies. H₂S producing organisms appear as colonies with black centers because of the presence of ferric citrate which forms iron sulphide. Bile salts inhibits most of Gram positive bacteria. Non fermenting Salmonella and Shigella colonies are blue green. The additional carbohydrate (sucrose) and salicin with the high concentration of peptones give better growth of Salmonella and Shigella spp.

Composition per liter:

Peptones…………………………………………11.500g

Yeast extract……………………………………...3.000g

Sodium chloride……………………………….....5.000g

Agar……………………………………………..12.000g

Lactose………………………………………….10.000g

Saccharose……………………………………....10.000g

Bile salt no. 3.……………………………………9.000g

Sodium thiosulphate……………………………..5.000g

Salicin……………………………………………2.000g

Ferric ammonium citrate………………………...1.500g

Acid fuchsin……………………………………..0.100g

Bromthymol blue………………………………..0.064g

Final pH of the ready to use medium:   7.5 ± 0.2

Medium preparation:  Add 69.1 grams of dehydrated culture medium to 1 liter of distilled water. Heat with repeated stirring and boil for one minute to dissolve completely. DO NOT AUTOCLAVE OR OVERHEAT THIS MEDIUM. Pour plates can be prepared after the medium has cooled to 45-50^oC.

Quality specifications:  Dehydrated medium:  homogeneous, light greenish-beige fine powder. Ready to use medium:  clear to trace hazy and light to dark green in color.

Microbiological response:

Storage: Dehydrated medium should be stored between 10 to 25^oC. Once opened, place the container in a dark, dry place. The dehydrated medium should not be used if there is any lump or the color has changed from the original.