Method for isolation and identification of Escherichia coli 0157:H7 and plating media for said process

A method of detecting the presence of Escherichia coli 0157:H7 in a test sample that contains other bacterial strains including other Escherichia coli strains comprising the steps of inoculating a solid plating medium with said sample, wherein said plating medium comprises at least one carbohydrate that is a member of the group sorbitol, salicin, inositol, adonitol, mannitol, dulcitol, d-sorbitol, L-arabinose, L-rhamnose, d-xylose, trehalose, d-mannose, and melibiose, Escherichia coli 0157:H7 being incapable of fermenting said carbohydrate but other strains of Escherichia coli fermenting said carbohydrate, a pH indicator dye that changes the color of the plating medium to a first color when the pH of the medium changes, a chromogenic substrate that reacts to beta-galactosidase to form a precipitate in the plating medium of a second color which contrasts with the first color, whereby a microorganism which ferments the carbohydrate but does not produce beta-galactosidase will produce colonies in the plating medium of the first color, a microorganism which does not ferment the carbohydrate but produces beta-galactosidase including Escherichia coli 0157:H7 will produce colonies in the plating medium of the second color, and microorganisms which ferment the carbohydrate and produce beta-galactosidase including the other strains of Escherichia coli will produce colonies in the plating medium of a third color which is the color that results from the mixing of the first and second colors, and a sufficient mass of an agent to solidify the mixture, thereafter incubating said plating medium for a sufficient period to obtain colonies of bacterial strains producing one or more of said colors, and examining the plating medium for colonies of said first second and third colors.

An isolation plating medium for use in processes for the presumptive identification of Escherichia coli 0157:H7 from a test sample that also contains other bacteria including other strains of Escherichia coli, both Escherichia coli 0157:H7 and the other strains of Escherichia coli being beta-galactosidase producers during metabolism, comprising a nutrient base consisting of one or more members of the group tryptone, bacto-peptone, and proteose-peptone, tellurite, at least one carbohydrate, said carbohydrate being a member of the group sorbitol, salicin, inositol, adonitol, mannitol, dulcitol, d-sorbitol, L-arabinose, L-rhamnose, d-xylose, trehalose, d-mannose, and melibiose, Escherichia coli 0157:H7 being incapable of fermenting said carbohydrate but other strains of Escherichia coli fermenting said carbohydrate, a pH indicator dye that changes the color of the plating medium to a first color when the pH of the medium changes, a chromogenic substrate that reacts to beta-galactosidase to form a precipitate in the plating medium of a second color which contrasts with the first color, said substrate being a member of the group indoxyl-beta-D-galactopyranoside and 5-bromo-4-chloro-3 -indoxyl-beta-D-galactopyranoside, whereby a microorganism which ferments the carbohydrate but does not produce beta-galactosidase will produce colonies in the plating medium of the first color, a microorganism which does not ferment the carbohydrate but produces beta-galactosidase including Escherichia coli 0157:H7 will produce colonies in the plating medium of the second color, and microorganisms which ferment the carbohydrate and produce beta-galactosidase including the other strains of Escherichia coli will produce colonies in the plating medium of a third color which is the color that results from the mixing of the first and second colors, and a sufficient mass of an agent to solidify the mixture.