Patent ID: 7150977

Claim:
A differential plating medium for the detection of Salmonella bacteria from a sample likely to contain Salmonella bacteria and other bacteria, said other bacteria releasing the enzyme beta-galactosidase on exposure to a substrate in the plating medium, comprising a mixture of (1) a carbohydrate that is a metabolic source for Salmonella bacteria, the metabolic reaction between Salmonella bacteria and the carbohydrate releasing acid into a portion of the medium of the reaction, (2) a pH indicator dye that changes the color of said portion of the plating medium to a first color different from the color of the medium responsive to a change in the pH of said portion of the medium, (3) a first substrate that does not react with Salmonella bacteria but reacts with the enzyme beta-galactosidase to produce a second color in the medium where it is acted upon by the enzyme beta-galactosidase, the second color contrasting with the first color and the color of the medium, (4) a second substrate that does not react with Salmonella bacteria but reacts with the enzyme beta-galactosidase to produce said second color in the medium where it is acted upon by the enzyme beta-galactosidase of, the first substrate reacting with the enzyme beta-galactosidase in a significantly shorter time than the second substrate, whereby colonies of said other bacteria contain the second color, and (5) an ingredient for thickening the mixture in sufficient quantity to solidify the mixture, wherein the first substrate and the second substrate are selected from the group consisting of 5-bromo-4-chloro-3-indoxyl-beta-D-galactopyranoside, 5-bromo-6-chloro-3-indoxyl-beta-D-galactopyranoside, 3-indoxyl-beta-D-galactopyranoside, 6-chloro-3-indoxyl-beta-D-galactopyranoside, 4-nitrophenyl-beta-D-galactopyranoside, 2-nitrophenyl-beta-D-galactopyranoside, 5-iodo-3-indoxyl-beta-D-galactopyranoside, 4-methylumbelliferyl-beta-D-galactopyranoside and N-methylindoxyl-beta-D-galactopyranoside.