Final answer:
Media that are both selective and differential are crucial in microbiology for promoting the growth of desired microorganisms while suppressing others, and for differentiating them based on biochemical properties like lactose fermentation on MacConkey agar.
Step-by-step explanation:
The advantages of a medium that is both selective and differential are significant in the field of microbiology. A selective medium, such as MacConkey agar, contains substances like bile salts and crystal violet that suppress the growth of certain bacteria while promoting the growth of others, like gram-negative enteric bacteria. This selectivity reduces competition and allows the enrichment of the desired microorganisms.
On the other hand, a differential medium provides a way to differentiate between microorganisms based on visual cues such as color changes, which arise from the metabolic activities of the organisms.
When a medium is both selective and differential, it can simultaneously enrich for specific bacteria and allow for their identification based on their biochemical properties and interactions with the medium's substrates.
A combined selective and differential medium is exemplified by MacConkey agar when used for the isolation and differentiation of enteric bacteria. Lactose fermenters like E. coli produce acid, turning the colonies and the medium hot pink, whereas non-fermenters do not induce this color change, simplifying the identification process.
The use of such media is crucial for tasks such as detecting bacterial contaminants in food. While these culture methods may take more time compared to rapid DNA or antibody testing, they offer a high level of specificity and sensitivity.