Final answer:
Selecting and differential media are combined into one agar to efficiently isolate and identify different bacteria in a single step by inhibiting unwanted microorganisms and distinguishing others based on growth patterns and colony color.
Step-by-step explanation:
Combining selective and differential media into one agar is an efficient way to isolate and identify bacteria. Selective media such as MacConkey agar inhibit the growth of certain microorganisms like many gram-positive bacteria, and support the growth of others like gram-negative enterics, by including selective agents like bile salts and crystal violet. Meanwhile, differential media differentiate between bacteria based on growth patterns, colony color, or changes in the medium itself due to bacterial metabolism. This could be observed through reactions such as the fermentation of lactose on MacConkey agar, where lactose fermenters produce acid, turning the medium and colonies pink. The neutral red pH indicator in the agar facilitates this visualization.
Such media can simplify the identification of bacteria in clinical and research settings by allowing technicians to both select for the growth of specific bacteria and differentiate among them in a single step. Tryptic Soy medium, given as an example, is a complex medium used for basic culturing techniques and does not contain selective or differential properties. In contrast, using combined selective and differential media can significantly speed up the biochemical identification process.