A
solid plating medium for the presumptive detection of
Escherichia coli 0157:H7 which comprises (1) an ingredient which promotes growth of
Escherichia coli cells under incubation, (2) an ingredient which inhibits growth of
gram positive microorganisms under incubation, (3) an ingredient that inhibits growth of
Proteus sp. under incubation, (4) an ingredient which inhibits the growth of strains of
Escherichia coli other than
Escherichia coli 0157:H7 under incubation, (5) a
carbohydrate medium that under incubation is not fermented by
Escherichia coli 0157:H7 but which is fermented by other microorganisms including other strains of
Escherichia coli, (6) a
pH indicator dye which changes the plating media to a first color when the pH of the medium changes, (7) a
chromogenic beta-galactosidase substrate that produces precipitate of a second color responsive to beta-galactosidase, the first color contrasting with the second color and the first and second colors blending to produce a third color which contrasts with the first and second colors, and (8) a
mass of
agar sufficient to solidify the mixture. Also, the method of detecting the presence of Escherichia coli 0157:H7 comprising inoculating the
solid plating medium set forth above with a
test sample containing Escherichia coli including Escherichia coli 0157:H7, then incubating said plating medium for a period sufficient to obtain colonies of microorganisms and generating one or more of the colors produced by the plating medium, and then examining the surface of the medium for the presence of colonies of the second color.