Final answer:
A differential medium is a culture medium that distinguishes between different microorganisms based on their biochemical characteristics, often observed through changes in the appearance of colonies or the medium upon bacterial growth.
Step-by-step explanation:
Define Differential Medium and Discuss Its Purpose
A differential medium is a type of bacteriological culture medium that is used to distinguish between different microorganisms based on their biochemical characteristics. The purpose of a differential medium is to differentiate between different microorganisms, which can be seen through distinct growth patterns, colony colors, or changes in the medium itself, often prompted by the metabolic processes of the organisms. As bacteria grow on such a medium, they display specific features or cause reactions that give them unique appearances enabling a microbiologist to distinguish between them.
For example, MacConkey agar is a commonly used differential medium that contains the pH indicator neutral red and components such as lactose, allowing differentiation of lactose-fermenting enteric bacteria, whose colonies turn hot pink, from non-fermenters, which remain colorless or take on a different hue.
To clarify options provided in the question: Option A refers to a general all-purpose medium which is not differential. Option B refers to a selective medium, which inhibits the growth of specific organisms but is not necessarily differential. Option D pertains to enriched media designed for fastidious bacteria, which also does not inherently differentiate between bacterial types.