noun

A medium used to screen for enteric bacteria by testing an organism's ability to ferment sugars and produce hydrogen sulfide. The medium is prepared as an agar slant which contains glucose, sucrose, lactose, phenol red, sodium thiosulfate and ferrous sulfate. The test is performed by inoculating the medium on the surface of the slant and by stabbing into the solid agar butt. The medium is then incubated and then examined. Fermentation of multiple sugars is indicated by yellowing of the entire medium (due to phenol red dye turning yellow as a result of acid formation). Fermentation of glucose alone is indicated by yellowing of only the agar butt. Hydrogen sulfide production is indicated by the formation of a black precipitate (the result of hydrogen sulfide reacting with ferrous sulfate). No change to the reddish color of the medium indicates a negative result.