Part of Thermo Fisher Scientific
Organisms this product works with:
Other products used in the isolation of Escherichia coli:
LAURYL TRYPTOSE BROTH (LAURYL SULPHATE BROTH)
a medium for the detection of coliform organisms in water and waste water, according to the formula of the American Public Health Association
Dipotassium hydrogen phosphate
Potassium dihydrogen phosphate
Sodium lauryl sulphate
pH 6.8 ± 0.2 @ 25°C
Dissolve 35.6g in 1 litre of distilled water and distribute into containers with fermentation tubes (Durham). Sterilise by autoclaving at 121°C for 15 minutes.
Lauryl Tryptose Broth provides a selective medium which is used for the detection of coliform organisms in water, dairy products and other foods. The APHA1 recommend that Lauryl Tryptose Broth should be used for the Most Probable Number (MPN) presumptive test of coliforms in waters, effluent or sewage as a confirmatory test of lactose fermentation with gas production for milk samples ( APHA2 ) and for the detection of coliforms in foods ( APHA3 ).
Surface active agents have long been used as the inhibitory ingredients in selective media. MacConkey4 introduced bile salts for this purpose and later Albus and Holm3 working with lactobacilli found that sodium ricinoleate exerted a selective action. The development of synthetic wetting agents opened up new fields of investigation. Mallmann and Darby6 after comparative tests with a large number of these compounds, showed that sodium lauryl sulphate gave the best results in selective media for the coliform group.
Lauryl Tryptose Broth was designed to promote a rich growth and copious gas production from small inocula of coliform organisms. Aerobic sporing bacteria are completely inhibited. The advantage in using this product is that in addition to giving the fermentation reaction typical of MacConkey Broth it can also be directly tested for the presence of indole. Unlike MacConkey Broth, the medium contains no indicator, but this can be added (if required) after incubation.
Lauryl Tryptose Broth is recommended for the detection and enumeration of coliform organisms in water and milk products, especially in the control of ice-cream manufacture and in dairy hygiene. A suggested procedure ( Dyett7 ) is as follows:
The addition of 4-methylumbelliferyl-ß-D-glucuronide (MUG) (BR0071) to this medium will enhance the detection of E. coli. Lauryl Tryptose Broth with MUG is also available from Oxoid (CM0980). The use of this medium in a Most Probable Number (MPN) technique for enumeration of presumptive Escherichia coli in milk and milk products has been specified in a standard procedure8.
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 room temperature.
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured solution
Expected result at 35°C
Escherichia coli ATCC® 25922 *
Turbid growth; gas
Staphylococcus aureus ATCC® 25923*
Inhibited or no growth
If stored at 2-8°C the broth will become cloudy or form a precipitate. This should clear at room temperature but gas formation is the criterion of growth not turbidity.
1. American Public Health Association (1980) Standard Methods for the Examination of Water and Wastewater. 15th Edn. APHA Inc. Washington DC.
2. American Public Health Association (1978) Standard Methods for the Examination of Dairy Products. 14th Edn. APHA Inc. Washington DC.
3. American Public Health Association (1976) Compendium of Methods for the Microbiological Examination of Foods. APHA Inc. Washington DC.
4. MacConkey A. T. (1938) J. Hyg. 8. 322-334.
5. Albus W. R. and Holm G. E. (1926) J. Bact. 12. 13-18.
6. Mallmann W. L. and Darby C. W. (1941) Am. J. Pub. Hlth. 31. 127-134.
7. Dyett E. J. (1957) Lab. Prac. 6(6). 327-328.
8. ISO Standard 11866-2 Milk and Milk Products - Enumeration of presumptive Escherichia coli - part 2: Most probable number technique using 4- methylumbelliferyl-ß-D-glucuronide.