a medium containing peptone, lactose, dipotassium phosphate, agar, sodium sulfite, basic fuchsin, and distilled water; originally developed for the isolation of Salmonella typhi, this medium is now most useful in the bacteriological examination of water; coliform organisms ferment the lactose, and their colonies become red and colour the surrounding medium; non-lactose-fermenting organisms produce clear, colourless colonies against the faint pink background of the medium