HEA contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria.

Use of these plates assumes that the user is not interested in other enteric pathogens such as Klebsiella or Escherichia.

Peptone metabolism by Shigella and Salmonella alkalises the medium, turning a pH indicator blue.

Most of these are inhibited on HEA plates by the inclusion of bile salts, so encountering a black colony that is not Salmonella is unusual, although not unheard of.

Those that are may be identified as red or yellow colonies with a black centre, indicating that they are fermenting sugar and probably not Salmonella.