Chromocult^® Tryptone Bile X-glucuronide agar

Chromocult^® Tryptone Bile X-glucuronide agar is a selective medium for the enumeration of Escherichia coli. The presence of the enzyme β-D-glucuronidase differentiates most E. coli from other coliforms. E. coli absorbs the chromogenic substrate 5-bromo-4-chloro-3- indolyl-β-D-glucuronide (X-β-D-glucuronide) while, the enzyme β-glucuronidase splits the bond between the chromophore 5-bromo-4-chloro-3-indolyl and the β-D-glucuronide. The formed E. coli colonies are colored blue to blue green. The growth of accompanying Gram-positive flora is largely inhibited due to the presence of bile salts and the high incubation temperature of 44°C. Some E. coli (3-4 %) are β-D-glucuronidase negative and appear as colorless colonies (e.g. most E. coli O157 strains) or do not grow at the elevated temperature of 44°C (e.g. E. coli 0157:H7).

Chromocult^® Tryptone Bile X-glucuronide agar is used for the enumeration, detection, and identification of β-glucuronidase positive Escherichia coli from food and feeding stuff, as well as from environmental samples in the area of food production and food handling.

Appearance (clearness): clear
Appearance (colour): yellowish to yellowish-brown
pH-value (25 °C): 7.0 - 7.4
Growth promotion test in accordance with the current version of DIN EN ISO 11133.
Inoculum on reference medium (Escherichia coli ATCC 8739 (WDCM 00012)):
Inoculum on reference medium (Escherichia coli ATCC 25922 (WDCM 00013)):
Inoculum on reference medium(Escherichia coli NCTC 13216 (WDCM00202)):
Colony count (Escherichia coli ATCC 8739 (WDCM 00012)):
Colony count (Escherichia coli ATCC 25922 (WDCM 00013)):
Colony count (Escherichia coli NCTC 13216 (WDCM00202)):
Recovery on test medium (Escherichia coli ATCC 8739 (WDCM 00012)): ≥ 50 %
Recovery on test medium (Escherichia coli ATCC 25922 (WDCM 00013)): ≥ 50 %
Recovery on test medium(Escherichia coli NCTC 13216 (WDCM00202)): ≥ 50 %
Growth (Enterococcus faecalis ATCC 19433 (WDCM 00009)): total inhibition
Growth (Enterococcus faecalis ATCC 29212 (WDCM 00087)): total inhibition
Growth (Citrobacter freundii ATCC 43864 (WDCM 00006)): no limit
Growth (Pseudomonas aeruginosa ATCC 27853 (WDCM 00025)): no limit
Colonies (Escherichia coli ATCC 8739 (WDCM 00012)): turquoise to blue
Colonies (Escherichia coli ATCC 25922 (WDCM 00013)): turquoise to blue
Colonies ((Escherichia coli NCTC 13216 (WDCM00202)): turquoise to blue
Colonies (Citrobacter freundii ATCC 43864 (WDCM 00006)): white to green-beige
Colonies (Pseudomonas aeruginosa ATCC 27853 (WDCM 00025)): white to green-beige
Incubation: 21 ± 3 hours at 44 ± 1 °C aerobic
A recovery rate of 50 % is equivalent to a productivity value of 0.5.
The indicated colony counts result from the sum of a triple determination.
Reference media: Tryptic Soy Agar

CHROMOCULT is a registered trademark of Merck KGaA, Darmstadt, Germany