Final answer:
To differentiate Salmonella from Citrobacter, the Voges-Proskauer (VP) test is used, which detects the production of acetoin, with Salmonella usually testing negative and some Citrobacter species testing positive. The correct option is d.
Step-by-step explanation:
The question is asking for the correct test used to differentiate Salmonella from Citrobacter. In the context of microbiology, especially when working with bacteria of the Family Enterobacteriaceae, a set of tests known as the IMVIC tests are often employed.
These tests are used to identify and differentiate bacteria by their biochemical characteristics. Among the IMVIC tests, the Voges-Proskauer (VP) test is the one that stands out for this purpose. The VP test detects acetoin production during glucose fermentation.
Salmonella species typically do not produce acetoin whereas some Citrobacter species do, which is evidenced by a reddish-brown color after adding the appropriate reagents in the VP test. The correct option is d.