Modified Tergitol Agar Base w/ 1.0% Agar

Intended Use

Modified Tergitol Agar Base w/1.0% Agar is used for the detection and enumeration of coliform and heat-tolerant bacteria in water from different sources by membrane filter method.

Composition**

Final pH ( at 25°C): 7.2±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 51.15 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. Add 2.5 ml of 1% 2,3,5 Triphenyl Tetrazolium Chloride (TTC) (FD057). Mix well and pour into sterile Petri plates.

Principle And Interpretation

Tergitol 7 Agar is a selective and differential medium for the detection and enumeration of coliforms in water. Chapman (1,2) modified his original formula of Tergitol 7 Agar by addition of Triphenyl Tetrazolium Chloride (TTC). Media with similar composition (with 15- 25 grams agar) is also recommended by ISO Committee (3).

Tergitol 7 acts as a selective agent (4) which inhibits gram positive organisms and minimises swarming of Proteus species enabling better coliform recovery. Lactose fermentation is observed by change in colour of bromo thymol blue, the pH indicator. Triphenyl Tetrazolium Chloride (TTC) allows earlier recognition and identification of Escherichia coli and Enterobacter aerogenes in water and food (5). TTC is rapidly reduced by coliforms except Escherichia coli and Enterobacter aerogenes to insoluble formazan which gives red colour to the colonies. The lactose fermenters show greenish yellow colonies with yellow zones while lactose non-fermenters show red colonies surrounded by blue zones.

Quality Control

Appearance: Cream to pale green homogeneous free flowing powder

Gelling: Firm, comparable with 1.0% Agar gel

Colour and Clarity of prepared medium: Green coloured, clear to slightly opalescent gel forms in Petri plates

Reaction: Reaction of 5.1% w/v aqueous solution at 25°C. pH : 7.2±0.2

pH: 7.00-7.40

Cultural Response

M1699: Cultural characteristics observed after an incubation at 35-37°C for 18-48 hours.

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.

Reference

1. Chapman G.H., 1947, J. Bact., 53:504.
2. Chapman G.H., 1951, Am. J. Public Health, 41:1381.
3. International Organization For Standardization (ISO), 1990, Draft ISO/DIS 9308-1.
4. Pollard A.L., 1946, Science., 103:758.
5. Mossel D.A.A., 1962, J. Appl. Bact., 25:20.