m-TEC Agar

In 1981 Dufour et al. developed a simple membrane filtration technique for rapid enumeration of E. coli, which quantified E. coli within 24 hours without requiring subculturing and identification of isolates.

Enzymatic digest of animal tissue provides nitrogen, carbon, and minerals essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Lactose is the fermentable carbohydrate providing carbon and energy. Potassium phosphate is a buffering agent. Sodium deoxycholate inhibits growth of Gram-positive bacteria. Sodium lauryl sulphate partially inhibits organisms other than coliforms. Bromocresol purple and bromophenol red are pH indicators. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 45.3 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Urea substrate

Combine 2 g of urea and 10 mg of phenol red in 100 mL of distilled water. Adjust pH to 5.0 ± 0.3.

Instructions for use

Membrane filter technique:

1. Filter an appropriate volume of sample through a 0.45 µm membrane.
2. Place the membrane onto the surface of an agar plate, avoiding the formation of air bubbles.
3. Invert the plates and incubate at 44.5 ± 0.5 °C for 22 ± 2 hours.
4. Place a sterile absorbent pad into a Petri dish.
5. Add approximately 2 mL of urea substrate to the pad (the pad should be saturated with urea substrate without any standing liquid in the Petri dish).
6. Transfer countable membrane filters to the pads saturated with urea substrate.
7. After 15-20 minutes, count all yellow, yellow-green to yellow-brown colonies.

• Clesceri L. S., Greenberg A. E. and Eaton A. D., (Ed.), 1998, Standard Methods for the Examination of Water and Wastewater, 20th Ed., American Public Health Association, Washington, D.C.
• Dufour A. P., Strickland E. R. and Cabelli V. J., 1981, Appl. Environ. Microbiol., 41: 1152