question
Selective Media Basics...
answer
Inhibits growth of unwanted organisms
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Selective Media Examples...
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Thayer Martin: Isolates Neisseria Gonorrhoea
MacConkey Agar: Isolates Gram Negative Bacteria
MacConkey Agar: Isolates Gram Negative Bacteria
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Differential Media Basics
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Contain substance that bacteria can change in a recognizable way.
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Differential Example:
answer
Blood Agar: certain products produce Hemolysin to break down red blood cells
MacConkey Agar: Indicates bacteria that produce acid
MacConkey Agar: Indicates bacteria that produce acid
question
Is MacConkey Agar selective or differential?
answer
Both
Selects for: gram negative
Indicates: bacteria which produce acid
Selects for: gram negative
Indicates: bacteria which produce acid
question
What are the three classes of Hemloysis?
answer
1. Gamma
2. Beta
3. Alpha
2. Beta
3. Alpha
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What is Gamma Hemolysis?
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Gamma = no lysis
Blood plate will remain fairly similar
Blood plate will remain fairly similar
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What is Beta Hemolysis?
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Beta = Complete Hemolysis (see through it)
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What does organisms do Beta Hemolysis?
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Group A strep
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What is alpha hemolysis?
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Alpha = Partial (green haze)
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What organisms produces Alpha Hemolysis?
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Strep Pneumo
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What is interesting about the use of sheeps blood in many laboratories?
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Sheep's blood will not yield any Beta Hemolysis.
Beta will be Alpha.
Thus in Sheep's Blood:
Alpha = Group A Strep
Beta will be Alpha.
Thus in Sheep's Blood:
Alpha = Group A Strep
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Is blood agar Differential or Selective?
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Purely Differential
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In MacConkey's agar, what changes do you look for and what does this signal?
answer
Will turn red if the organism is producing acid.
Acid production is a result of Fermentation.
Thus, if Red = Fermenter.
Acid production is a result of Fermentation.
Thus, if Red = Fermenter.
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What does EMB agar test for?
answer
Acid production via Lactose Fermentation.
E. Coli produces metallic green sheen.
E. Coli produces metallic green sheen.
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Blood agar is generally used to distinguish between what kind of Bacteria? (positive or negative)
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Negative
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Is Egg Yolk selective or differential?
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Differential
(C. perfinigens)
(C. perfinigens)
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Is Tellurite Selective or Differential?
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Both
(C. diptheriae)
(C. diptheriae)
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Is Triple Sugar Iron (TSI) selective or differential?
answer
Differential for:
Anaerobe vs Aerobe
Gas production
H2S
Anaerobe vs Aerobe
Gas production
H2S
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Compare Thayer-Martin vs. Chocolate Medium?
answer
Thayer Martin is Chocolate Medium treated with antibiotics.
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When would you use Thayer-Martin vs Chocolate Medium?
answer
Thayer-Martin would be used for an organism which comes from a potentially dirty source (Gonorea from urethra)
Chocolate Medium would be used for any organism from a clean source. (Meningitis from CSF)
Chocolate Medium would be used for any organism from a clean source. (Meningitis from CSF)
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What is a fastidious organism?
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Something that needs extra nutrients to grow?
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What are three examples of Fastidious organisms?
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Haemophilus
Legionella
Bordatella
Legionella
Bordatella
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Haemophilus requires what?
answer
X(heme) and V (NAD) on chocolate agar
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Legionalla?
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Charcoal Yeast --> Iron and Cystein
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Bordatella?
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Bordet-Gengou
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What is Lowenstein-Jensen Medium used for?
answer
Mycobacteria
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What other organisms will not grow?
answer
Mycoplasma
Spirochetes
Intracellular
M. leprae
Spirochetes
Intracellular
M. leprae
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What does the Catalase Test differentiate?
answer
Staph = positive
Strep = negative
Strep = negative
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