Lauryl Tryptose Broth is a selective medium for the detection of coliforms in water, dairy products and other foods. The American PublicHealth Authority (APHA) recommend Lauryl Tryptose Broth for the Most Probable Number Presumptive Test of coliforms in waters, effluent or sewage and as a confirmation test of lactose fermentation with gas production from milk samples and for the detection of coliforms in foods.
Lauryl Tryptose Broth is prepared according to the formulation of Mallmann and Darby. Mallmann and Darby showed that tryptose at a concentration of 2% increased the early logarithmic growth phase when compared to meat peptone. These researchers added phosphate buffers and sodium chloride, which improved gas production by «slow lactose fermenting» organisms. Sodium lauryl sulfate was incorporated as a selective agent for the inhibition of noncoliform organisms.