In the MPn Presumptive Phase, which statement about Lauryl Tryptose Broth is correct?

• A. Lauryl Tryptose Broth contains glucose.
• B. Lauryl Tryptose Broth contains lactose and is used for inoculation.
• C. Lauryl Tryptose Broth contains lactose-free.
• D. Lauryl Tryptose Broth does not contain lactose.

Answer: (B)

In this phase of the MPn test, the medium used to screen for lactose-fermenting coliforms must have lactose so that fermentation can be observed. Lauryl Tryptose Broth is designed with lactose as a key substrate and is the medium into which the sample is inoculated during the presumptive phase. If lactose-fermenting organisms are present, they produce gas, giving a positive presumptive result. That combination—lactose in the medium and the inoculation step to test the sample—matches the statement that best describes Lauryl Tryptose Broth.

The other possibilities don’t fit: the broth is not based on glucose and is not lactose-free, so those attributes are incorrect.