General description

Chromocult^® Coliform Agar ES is a selective and differential chromogenic culture medium intended for use in microbiology laboratories analyzing food and animal feeds. The modified Chromocult^® Coliform agar with enhanced selectivity allows the simultaneous detection of coliforms and E. coli in samples with high bacterial bioburden. A combination of suitable peptones and buffering with MOPS encourages rapid growth of coliforms and optimum transformation of the chromogenic substrates. The bile salts and propionate inhibit the growth of Gram-positive and Gram-negative accompanying flora. Simultaneous detection of total coliforms and E. coli is achieved by using a combination of two chromogenic substrates. The substrate Salmon-β-D-GAL is cleaved by β-D-galactosidase, characteristic for coliforms, resulting in a salmon to red coloration of coliform colonies. The substrate X-β-D-glucuronide is cleaved via β-D-glucuronidase, characteristic for E. coli, causing positive colonies to turn blue. As E. coli cleaves Salmon-β-D-GAL as well as X-β-D-glucuronide, its colonies turn dark violet and are easily differentiated from the other coliforms, these being salmon-red.

Application

Chromocult^® Coliform Agar is a selective agar suitable for the simultaneous detection and colony count of total coliforms and E. coli in foods. This medium enables E. coli and coliforms from food matrices such as raw ground beef, raw ground chicken, and raw milk to be detected, differentiated, and enumerated within 24 hours.

Analysis Note

Appearance (clearness): clear
pH-value (25 °C): 6.8 - 7.2
Recovery on test medium (Escherichia coli ATCC 11775 (WDCM 00090)): ≥ 70 %
Recovery on test medium (Citrobacter freundii ATCC 8090): ≥ 70 %
Recovery on test medium (Enterobacter aerogenes ATCC 13048): ≥ 70 %
Recovery on test medium (Proteus mirabilis ATCC 29906 (WDCM 00023)):
Growth (Aeromonas hydrophila ATCC 7966 (WDCM 00063)): inhibited
Growth (Enterococcus faecalis ATCC 19433 (WDCM 00009)): inhibited
Growth (Staphylococcus aureus ATCC 25923 (WDCM 00034)): inhibited
Growth (Bacillus subtilis ATCC 6633 (WDCM 00003)): inhibited
Colony colour (Escherichia coli ATCC 11775 (WDCM 00090)): blue
Colony colour (Citrobacter freundii ATCC 8090): pink-red
Colony colour (Enterobacter aerogenes ATCC 13048): pink-red
Incubation: 24 hrs.; 35 °C; aerobic.
Reference: Tryptic soy agar.
Inhibited strains tested with three-loop-streak.