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MODIFIED LAURYL SULPHATE TRYPTOSE BROTH WITH MUG

Code: CM0967

A modified Lauryl Tryptose Broth, incorporating 4-methylumbelliferyl-ß-D-glucuronide (MUG) allowing the enumeration of presumptive Escherichia coli as well as other coliforms, using the Most Probable Number (MPN) method.

Directions
Dissolve 36.7g of Modified Lauryl Sulphate Tryptose Broth with MUG in 1 litre of distilled water.
Dispense into final containers containing Durham tubes.
Sterilise by autoclaving at 121°C for 15 minutes.

Description
Oxoid Modified Lauryl Sulphate Tryptose Broth with MUG is formulated to allow use of the MPN technique for coliforms and also the enumeration of presumptive Escherichia coli by means of a culture technique involving a liquid medium containing MUG.

The formulation contains 4-methylumbelliferyl-ß-D-glucuronide (MUG), which is cleaved by the enzyme ß-glucuronide to release 4-methylumbelliferone. This blue-green fluorophore exhibits blue-green fluorescence visible when viewed under long wave ultra-violet (366nm). The inclusion of tryptophan acts as a substrate for indole production. Both reactions are characteristic of Escherichia coli and can therefore be used to identify presumptive Escherichia coli.

NaOH addition generally improves fluorescence by increasing the alkalinity of the solution. An increase in fluorescence can also be achieved by increasing the level of MUG added to the base medium.

Coliform organisms will ferment lactose to produce gas. This production of gas can be taken as positive for the presence of coliforms.

Technique
Prepare a sufficient number of dilutions of original sample to ensure tubes for the final dilution will yield a negative result. Inoculate each dilution into tubes of Modified Lauryl Sulphate Tryptose Broth with MUG containing inverted Durham tubes. For the MPN technique, inoculate each dilution in triplicate.

Incubate the tubes at 30°C for 24-48 hours. Examine the tubes for growth turbidity, gas production, fluorescence and formation of indole. Read as follows:
1. Tubes showing fluorescence gas and formation of indole indicate presumptive Escherichia coli.
2. Tubes showing gas formation indicate coliforms.

The MPN index can be determined from the numbers of positive tubes of selected dilutions by means of an MPB table, and a calculation of the MPN of presumptive Escherichia coli or coliforms per gram or per millilitre of the original sample carried out.

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

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Staw coloured solution

Quality control

* This organism is available as a Culti-Loop®

References
1. IDF-170L (1994) Milie & Milie products. Enumeration of presumptive Escherichia coli.
2. ISO-11866-2: (1997) (E).