Podcast
Questions and Answers
What is the main purpose of the salt in MSA media?
What is the main purpose of the salt in MSA media?
- To provide a source of carbon for bacterial growth
- To emulsify fats in the medium
- To inhibit the growth of enteric bacteria
- To selectively encourage the growth of *Staphylococcus* species (correct)
What happens to the pH of MSA media when a bacterium ferments mannitol?
What happens to the pH of MSA media when a bacterium ferments mannitol?
- It remains unchanged and the medium stays red
- It increases and the medium turns blue
- It becomes neutral and the medium turns green
- It decreases and the medium turns yellow (correct)
Which ingredient in MacConkey Agar is responsible for inhibiting Gram-positive organisms?
Which ingredient in MacConkey Agar is responsible for inhibiting Gram-positive organisms?
- Mannitol
- Neutral red
- Crystal violet (correct)
- Bile salts
How does MacConkey Agar select for bile-resistant microorganisms?
How does MacConkey Agar select for bile-resistant microorganisms?
What is the role of neutral red in MacConkey Agar?
What is the role of neutral red in MacConkey Agar?
Flashcards
MSA Selective Properties
MSA Selective Properties
MSA selects for Staphylococcus species due to the presence of salt.
MSA Differential Properties
MSA Differential Properties
MSA differentiates Staphylococcus species that ferment mannitol from those that don't based on pH change.
MacConkey Agar Selectivity
MacConkey Agar Selectivity
MacConkey Agar selects for bile-resistant, primarily enteric bacteria by using bile salts.
MacConkey Agar Differentiation
MacConkey Agar Differentiation
Signup and view all the flashcards
Gram-positive inhibition
Gram-positive inhibition
Signup and view all the flashcards
Study Notes
MSA Media
- MSA media is both selective and differential
- Selective component: salt
- Differential component: mannitol
- Salt selects for Staphylococcus species
- Media differentiates Staphylococcus species that ferment mannitol from those that don't
- If a bacterium ferments mannitol (e.g., S. aureus), it lowers the medium's pH
- pH change is detectable because the media contains phenol red, which turns yellow at low pH
- If a bacterium does not ferment mannitol (e.g., S. epidermidis), the pH doesn't change and the medium remains red
MacConkey Agar
- MacConkey Agar is both differentiating and selecting
- Contains bile salts, which are found in the gut and help in digestion by emulsifying fats
- Enteric microbes constantly encounter bile salts and have developed mechanisms to prevent the salts from destroying their membranes
- Non-enteric microbes are more susceptible to bile salts and less likely to grow in their presence
- Therefore, MacConkey Agar selects for bile-resistant microorganisms
- Current recipe contains 2 extra ingredients to increase selectivity and make it differential:
- Addition of crystal violet inhibits growth of Gram-positive organisms
- Addition of neutral red, a pH indicator
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
