endo agar endo agar endo agar (also called endo's medium) is a microbiological growth medium with a faint pink colour. originally developed for the isolation of salmonella typhi, it is now used mostly as a coliform medium. most gram-negative organisms grow well in this medium, while growth of gram-positive organisms is inhibited. coliform organisms ferment the lactose in this medium, producing a green metallic sheen (i.e. escherichia coli), whereas non-lactose-fermenting organisms produce clear, colourless colonies, i.e. salmonella species. endo agar typical composition endo agar typically contains (w/v): 1.0 % peptone 0.25 % dipotassium hydrogen phosphate (k2hpo4) 1.0 % lactose 0.33 % anhydrous sodium sulfite (na2so3) 0.03 % fuchsine 1.25 % agar