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Explore the fascinating world of microbiology through this engaging exploration of differentiating media. Assess your understanding of how microorganisms are identified and distinguished in the lab. This flashcard boosts your...

Questions: 24 | Attempts: 10 | Last updated: Aug 4, 2025

Sample Question 1
What type of organisms does Phenylethyl Alcohol Agar (PEA) select for and inhibit?

Only selects for G+ orgs.

Only inhibits most G- orgs.

Selects for G- orgs and inhibits G+ orgs.

? Selects for G+ orgs • Inhibits most G- orgs. • Must compare growth to a control plate (EMB, MAC, BHI or TSA) ? Results – • Growth compared to control = (+) • No growth or Inhibited growth = (-) NA PEA

Sample Question 2
What is the purpose of Mannitol Salt Agar (MSA)?

? Differential & selective • Selects for halophiles with high [salt] – 7.5% NaCl • Differentiates based on ability to ferment mannitol ? pH indicator = phenol red • Yellow = acid production = + fermentation ? Results • Growth or no growth (inhibited) • A= or Ahttp

Nutrient medium

Indicator for pH changes

Selective for acidophiles

Sample Question 3
What is the purpose of MacConkey Agar (MAC) in microbiology?

Only selective

Only differential

Only used for G(+) organisms

? Selective • Selects for Gram (-) – Crystal violet & bile salts inhibit G(+) ? Differential • Ability to ferment lactose • pH indicator = neutral red, turns pinkish/red when pH < 6.8 ? Results – Compare to PEA for control • Orgs that ferment lactose ? red growth (Differential) • Non-fermenters produce non-colored colonies • Inhibited/No growth = (-) (Indicates G+ organism)