Tryptone Bile X (TBX) Agar

Recent developments in culture media have given rise to the use of chromogenic substrates as a means of differentiating bacteria.

particularly among the coliform group of organisms. This is one such medium and has been developed as a selective medium for the isolation and enumeration of Escherichia coli without the need for membranes or pre-incubation.

Based on the formulation of Tryptone Bile Agar it incorporates a chromogenic substrate, X-Glucuronide, to detect the ß-glucuronidase enzyme which is specific for the majority of E. coli strains. Approximately, 3-4% of E. coli are glucuronidase negative including E. coli O157.(1)

The advantage of the chromogenic substrate is that the reaction is concentrated within the colony resulting in distinctive blue/green colonies of E. coli while the other coliforms produce cream colonies.

Selective medium for the isolation and enumeration of Escherichia coli without the need for membranes or pre-incubation.

Shelf Life (days)
1095 days

Storage Temp (°C)
10-30°C

Dehydrated Medium Appearance
Fine Powder

Prepared Medium Appearance
Firm Gel

Dehydrated Medium Colour
Beige

Prepared Medium Colour
Straw

Dehydrated PH
7.2 ± 0.2

Prepared PH
7.2 ± 0.2

Recommended Incubation
Aerobically for 18-24 hours at 44°C ± 1°C

FORMULA* g/L

Tryptone: 20

Bile salts no: 3 1.5

X-Glucuronide: 0.075

Agar: 15

Total: 36.6