Lauryl tryptose broth

Lauryl Tryptose Broth is a selective medium used in microbiology for the detection and enumeration of coliform bacteria, which are a common indicator of sanitary quality of foods and water. Coliforms are defined as rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35-37°C. Lauryl Tryptose Broth, with its specific composition, provides an optimal environment for the growth of coliforms, while inhibiting the growth of non-coliform bacteria.

Composition

The broth contains tryptose, which serves as a source of amino acids for the bacterial growth. Lactose is included as the fermentable carbohydrate for the detection of coliforms. Lauryl sulfate acts as a selective agent, inhibiting the growth of Gram-positive bacteria. The medium also contains a pH indicator that changes color when acid is produced from lactose fermentation. The exact composition may vary slightly between manufacturers, but the primary components remain consistent.

Principle

The principle behind Lauryl Tryptose Broth is to provide a selective medium that favors the growth of coliform bacteria by providing essential nutrients and a suitable pH environment. The presence of lauryl sulfate inhibits the growth of non-target bacteria, allowing for a more accurate detection of coliforms. When coliform bacteria ferment lactose, acid and gas are produced, leading to a change in the color of the pH indicator and the formation of gas bubbles in a Durham tube, if used.

Procedure

A sample is inoculated into Lauryl Tryptose Broth and incubated at 35-37°C for 24-48 hours. A positive result is indicated by the production of gas, observed as bubbles in the Durham tube, and/or a color change in the medium due to acid production. Further confirmatory tests are required to identify the specific type of coliform bacteria present.

Applications

Lauryl Tryptose Broth is widely used in the water quality testing of drinking water, wastewater, and recreational waters, as well as in the food industry for testing dairy products, non-alcoholic beverages, and other food items. Its ease of use and reliability make it a standard method for initial screening for coliform bacteria.

Limitations

While Lauryl Tryptose Broth is effective for the detection of coliforms, it does not differentiate between species of coliform bacteria. Further, some strains of coliforms may not grow well in this medium, leading to false negatives. Therefore, positive results should always be confirmed with additional tests.

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