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Questions and Answers
Which type of media allows a specific organism to grow while inhibiting the growth of most others?
Which type of media allows a specific organism to grow while inhibiting the growth of most others?
- Differential media
- Selective media (correct)
- Enriched media
- Nutritional media
What is the primary characteristic of blood agar as a differential medium?
What is the primary characteristic of blood agar as a differential medium?
- It contains antibiotics to inhibit specific bacterial growth.
- It allows visual differentiation based on hemolysis patterns. (correct)
- It is used to select for organisms in low pH environments.
- It promotes the growth of only gram-positive bacteria.
How does mannitol salt agar inhibit the growth of most bacteria?
How does mannitol salt agar inhibit the growth of most bacteria?
- By providing a limited supply of essential nutrients.
- By incorporating antibiotics that target gram-negative bacteria.
- By having a high salt concentration. (correct)
- By lowering the pH of the medium dramatically.
If an organism shows no color change in blood agar, what does this indicate about its hemolytic activity?
If an organism shows no color change in blood agar, what does this indicate about its hemolytic activity?
What distinguishes partial hemolysis in Streptococcus species when grown on blood agar?
What distinguishes partial hemolysis in Streptococcus species when grown on blood agar?
Flashcards
Selective media
Selective media
Media that stops the growth of most organisms, letting only specific types grow.
Mannitol salt agar (MSA)
Mannitol salt agar (MSA)
Selective media using high salt concentration to stop most bacteria besides Staphylococcus species.
Differential media
Differential media
Media that allows various bacterial species to grow, but their growth shows visual differences.
Blood agar
Blood agar
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Hemolysis
Hemolysis
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Study Notes
Selective Media
- Selective media contain substances inhibiting the growth of certain organisms while allowing others to grow
- Mannitol salt agar (MSA) has high salt concentration, inhibiting most organisms except Staphylococcus species. This is due to brnQ, arsR, and cardiolipin
- Selective media can also prevent specific organisms based on criteria such as amino acid composition or pH
Differential Media
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Differential media allow various bacterial species to grow, but their growth patterns differ visually.
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Blood agar is a common differential medium, requiring 5-10% sheep or horse blood for certain Streptococcus species.
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Different Streptococcus species break down blood cells (hemolysis) in varying ways, presenting different appearances.
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No media color change = no blood cell lysis (S. veridans)
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Green/brown media = partial blood cell lysis (S. haemolyticus)
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Lightened agar around bacterial growth = complete blood cell lysis (S. pyogenes)
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