This is a Provisional monograph.

M-Endo agar was originally formulated by McCarthy et al. (1961) as Endo agar LES (Lawrence Experimental Station). The original medium used two stages, incubating firstly on lauryl tryptose broth followed by transfer to Endo agar. It is based on the production of acetaldehyde from lactose fermentation rather than the production of acid. Basic fuchsin mixed with sodium sulfite gives fuchsin sulfite, which is colourless. Acetaldehyde production turns the reagent red, giving the characteristic red colonies of coliforms. APHA (2005) describes both the two-stage enrichment technique and direct inoculation of membranes onto either Endo broth or Endo agar