TERGITOL-7 AGAR

Code: CM0793

A selective medium for the detection and enumeration of coliforms.

Typical Formula*	gm/litre
Peptone	10.0
Yeast extract	6.0
Meat extract	5.0
Lactose	20.0
Bromothymol blue	0.05
Tergitol-7	0.1
Agar	13.0
pH 7.2 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards 

TTC Solution (SR0148) is supplied as 2ml of filtered 0.125% aqueous solution of tri-phenyltetrazolium chloride (TTC).

Directions
Suspend 54.15g in 1 litre of distilled water. Bring to the boil to dissolve completely. Dispense in 100ml volumes and sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C and add the contents of 1 vial of SR0148. Mix well and pour into sterile Petri dishes.

Description
Tergitol-7 Agar is a selective and differential medium for the detection and enumeration of coliforms in food and water samples.

Tergitol-7 Agar is based on the formulation described by Chapman¹ and is recommended for the selective isolation and differentiation of the coliform group. The use of Tergitol-7 as a selective agent had been described earlier².

The addition of tri-phenyltetrazolium chloride (TTC)³ allows earlier recognition and identification of Escherichia coli and Enterobacter aerogenes. This medium has been recommended for examining foodstuffs for faecal contamination⁴ and has been successfully used in routine water analysis⁵.

Tergitol-7 inhibits Gram positive organisms and minimises the swarming of Proteus allowing superior recovery of coliforms. Fermentation of lactose is seen by a change in colour of the pH indicator bromothymol blue. TTC is rapidly reduced to insoluble red formazan by most coliform organisms except Escherichia coli and Enterobacter aerogenes, thus allowing easy differentiation. Tergitol-7 Agar is quoted in the EU Directive for the detection and enumeration of coliforms in drinking water^6.

Technique
Inoculate by spreading the sample on the surface of the agar. Incubate at 35°C for up to 24 hours.

Escherichia coli	Yellow colonies with yellow zone Sometimes with rust coloured centre
Enterobacter/Klebsiella species	Greenish/yellow colonies
Salmonella species	Red colony with bluish zone
Shigella species	Red colony with bluish zone
Proteus species	Red colony with bluish zone
Pseudomonas species	Red colony with bluish zone
Gram positive bacteria	No growth to slight growth

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: Pale green coloured, free-flowing powder
Prepared medium: Dark green coloured gel

Quality control

Positive control:	Expected results
Escherichia coli ATCC® 25922 *	Good growth; yellow-orange coloured colonies with yellow zone
Negative control:
Staphylococcus aureus ATCC® 25923 *	Inhibited or no growth