Hektoen Enteric Agar | DM134

Hektoen Enteric Agar | DM134

A differential, selective medium for the isolation of Shigella and Salmonella

MAST Hektoen Enteric Agar is a selective medium for the isolation and differentiation of Shigella and Salmonella. The medium is based upon the work of King and Metzger (1968) at the Hektoen Institute for Medical Research (U.S.A.). They devised a medium which grew shigellae as readily as other pathogens, while inhibiting normal intestinal flora and which facilitated presumptive colonial recognition of enteric pathogens. The inhibition of shigellae by bile salts was reduced by the addition of increased carbohydrates and peptones and by the use of an indicator system of minimal toxicity. The ability of Hektoen Enteric Agar to grow shigellae and salmonellae has been confirmed by Taylor and Schelhart (1971).

2. Technical Formula*

3. Directions
1. Suspend by swirling 69.8g of powder in 1 litre of distilled or deionised water.
2. Allow to stand for 10-15 minutes.
3. Heat gently and boil for a few seconds until the agar dissolves. DO NOT AUTOCLAVE.
4. Cool to 55-60ºC, mix well and pour plates.

4. In Use

Inoculate the medium directly from the specimen or after enrichment in MAST Selenite F Broth (DM210). Streak with a wire
loop to obtain well isolated colonies. Incubate for 18-24 hours at 37ºC. Improved colonial differentiation between salmonellae and shigellae is achieved by prolonging the incubation period.
Colony Characteristics
Shigella spp./Providencia - green colonies.
Salmonella spp. - blue/green colonies with or without black centres.
Pseudomonas spp. - green/brown irregular colonies.
Coliforms - salmon-coloured colonies.