Use the following information to answer questions 1 and 2. Two culture media were inoculated with four different bacteria. After incubation, the following results were obtained:
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Medium 2 is
a. selective.
b. differential.
c. both selective and differential.

Verified step by step guidance

1. Understand the definitions: Selective media allow the growth of certain types of organisms, while inhibiting the growth of others. Differential media contain substances that cause some bacteria to take on an appearance that distinguishes them from other bacteria.
2. Examine the results from Medium 2: Look for evidence of growth inhibition or promotion of specific bacteria, which would indicate selectivity.
3. Check for visual differences in bacterial colonies on Medium 2: This would suggest that the medium is differential, as it allows for differentiation between bacteria based on appearance.
4. Determine if Medium 2 shows characteristics of both selective and differential media: If it inhibits some bacteria while allowing others to grow and also shows visual differences, it is both selective and differential.
5. Conclude based on the observations: Decide whether Medium 2 is selective, differential, or both, based on the presence of selective growth and/or visual differentiation.

Key Concepts

Selective Media

Selective media are designed to favor the growth of specific microorganisms while inhibiting the growth of others. This is achieved through the inclusion of certain chemicals or conditions that create an environment where only the desired organisms can thrive. For example, a medium containing antibiotics will allow only antibiotic-resistant bacteria to grow.

Differential Media

Differential media allow multiple types of microorganisms to grow but contain indicators that reveal differences between them. These indicators can change color or produce a precipitate in response to metabolic activities of the bacteria. For instance, a medium that changes color in the presence of acid produced by fermenting bacteria helps distinguish between lactose fermenters and non-fermenters.

Both Selective and Differential Media

Some media serve both selective and differential purposes, allowing specific bacteria to grow while also providing visual cues to differentiate between them. An example is MacConkey agar, which selects for Gram-negative bacteria and differentiates lactose fermenters from non-fermenters based on color change. Understanding these dual functions is crucial for interpreting experimental results in microbiology.