Lauryl Sulfate Broth (Lauryl Tryptose Broth LTB) is a selective medium recommended for the enumeration of coliforms in water and dairy products as well as for confirmatory tests of lactose fermentation with gas production by coliforms in foods. Another advantage of this medium is that the indole test can be performed directly in the tube. APHA recommends the use of Lauryl Tryptose Broth for the Most Probable Number Presumptive Test of coliforms in waters, effluent or sewage, also as a confirmatory test of lactose fermentation with gas production for milk samples, and for the detection of coliforms in foods. This broth was elaborated to promote a rich growth and high gas production from small inocula of coliform organisms. Lauryl Sulfate Broth is recommended by the norm ISO 4831 and ISO 7251 for the detection and enumeration of coliforms and E. coli respectively, by the most probable number technique. The coliform group is both aerobic and anaerobic, Gram-negative, non spore forming, and ferment lactose producing acid and gas at 35°C within 48 hours. Tryptose in a 2% concentration improves the early growth phase of coliforms when compared to Casein peptone. The buffered broth allows slow lactose fermenters to increase gas production in a shorter time. Tryptose provides nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is a fermentable complex carbohydrate energy source. Potassium phosphates are the buffering agents, and Sodium chloride supplies essential electrolytes for transport and osmotic balance. Sodium lauryl sulfate is the selective agent used to inhibit organisms other than coliforms. Sporulating aerobic bacteria are completely inhibited.
Write Your Own Review