Thermo Scientific™ Oxoid™ Typtone Bile X-Glucuronide (TBX) Medium (Dehydrated)

TBX Medium is a selective chromogenic medium designed for the detection and enumeration of beta-glucuronidase-positive Escherichia coli in food and animal feeding stuffs. It aligns with the ISO 16649 and ISO 11133 standards, ensuring high specificity and reliability in detecting E. coli contamination.

Key Features:

1. Chromogenic Agent:
   • Incorporates X-glucuronide, enabling visual identification of E. coli colonies as blue/green due to intracellular cleavage by beta-glucuronidase.
2. ISO Compliance:
   • Conforms to ISO 16649 parts 1, 2, and 3, as well as ISO 11133:2014 for culture media preparation and performance.
3. Highly Specific for E. coli:
   • Targets beta-glucuronidase-positive strains, except for a minority of strains like E. coli O157, which are glucuronidase-negative.
4. Versatile Application:
   • Suitable for food and animal feed testing for microbial safety and quality control.

Typical Formula (per liter):

Preparation Instructions:

1. Reconstitution:
   • Suspend 36.6 g of TBX Medium powder in 1 liter of distilled water.
2. Sterilization:
   • Autoclave at 121°C for 15 minutes.
3. Pouring Plates:
   • Cool the sterilized medium to 50°C, mix well, and pour into sterile Petri dishes.

Applications and Techniques:

1. Sample Preparation:
   • Homogenize food samples (e.g., 1:10 dilution) using a stomacher or blender in Maximum Recovery Diluent (CM0733).
2. Detection Techniques:
   • Direct Plating:
     • Spread 0.1 mL or 0.5 mL of homogenate onto TBX agar plates and incubate at 37°C or 44°C.
   • Membrane Method:
     • Place a cellulose membrane with homogenate on Minerals Modified Glutamate Agar, resuscitate at 37°C, then transfer to TBX plates for further incubation.
   • Pour Plate:
     • Add homogenate into a Petri dish, overlay with TBX agar (cooled to 45°C), and mix.
3. Incubation:
   • Incubate plates under the specified conditions for 18–24 hours.
4. Colony Enumeration:
   • Multiply the count of blue/green colonies by the dilution factor to determine E. coli concentration.

Quality Control:

Storage and Shelf Life:

Advantages:

Appearance:

Precautions:

• Approximately 3–4% of E. coli strains, including E. coli O157, are beta-glucuronidase-negative and may not produce blue/green colonies.
• Follow aseptic techniques during preparation and testing.

References:

1. ISO 16649-1:2001: Enumeration of beta-glucuronidase-positive Escherichia coli—Colony-count technique at 44°C using membranes and X-glucuronide.
2. ISO 16649-2:2001: Enumeration of beta-glucuronidase-positive Escherichia coli—Colony-count technique at 44°C.
3. ISO 16649-3:2015: Detection of beta-glucuronidase-positive Escherichia coli using most probable number techniques.
4. ISO 11133:2014: Preparation, production, storage, and performance testing of culture media.

Thermo Scientific™ Oxoid™ TBX Medium ensures reliable, ISO-compliant testing of Escherichia coli, offering a robust tool for food and animal feed microbiological analysis.