Lab Exam 3 Gram + Flashcards
Gram + test
You should memorzie a few potential species used for these tests.
- Aureus (Used in MSA)
- Epidermidis (Used in MSA)
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What two genera were used for these tests?
- Staphylococcus
- Streptococcus
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What does a positive result of the Selective and Differential test look like?
What does a negative result of the Selective and Differential test look like?
Think of the MSA plate and what color it is when it’s a positive result.
A positive result for the S&D test will result in a yellow color change. (Staphylococcus aureus)
A negative result for the S&D test will result in the plate remaining red. (Staphylococcus epidermidis)
Gram + test
What does a positive result look like when testing for coagulase production when using Vogel-Johnson agar? What does a negative result look like?
Think of the color of colonies that should show on the plate.
HINT: There are two tests; coagulase and mannitol fermentation
- Positive for coagulase = Black colonies
- Negative for coagulase = No black colonies
- Positive for Mannitol fermentation = Yellow zones around colonies
- Negative for Mannitol fermentation = No yellow ; plate remains red
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What does a positive result look like for hemolysin production when using Blood Agar? What does a negative result look like?
- Positive result: Red dissapearing from underneath the colonies (clearance zones). Known as Beta pattern.
- Negative result: Plate remains fully red, meaning there is no hemolysin. Known as a Gamma Pattern.
Gram + test
Is urea a product or reactant for this test?
Urea is a reactant for the urease test.
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What are the two products of the enzyme urease? Know how to write out the molecular formula of each of these products.
The two products are ammonia (NH3) and carbon dioxide (CO2).
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Which product of urease changes the pH of the sample tube?
Ammonia changes the pH of the sample tube.
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Will a tube that is positive for urease activity become more acidic or more alkaline?
A tube positive for urease activity will become more alkaline.
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What is the weak acid/weak base pair that is produced by urease activity?
Ammonium hydroxide (NH4OH).
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Which pH indicator is used in a urea agar slant?
Phenol red
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What color is a tube that is positive for urease activity?
Pink
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What is the name of the toxin that destroys red blood cells?
Hemolysin (exotoxin)
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What would a positive blood agar test result look like?
Clearance zones around bacterial colonies, indicating hemolysis.
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Which two Greek letters are used to describe a positive test result for Blood Agar?
Alpha (α) and beta (β).
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Which Greek letter is used to describe a negative test result?
Gamma (γ).
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What type of agar is used to screen for antibiotic sensitivity of our unknown?
TSA
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Which plating technique is used to prepare this plate for antibiotic resistance?
Lawn plate technique
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How does novobiocin inhibit bacterial growth?
By interfering with DNA replication.
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What would a positive test result for resistance look like?
No death zone
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What would a negative test result for resistance look like?
A death zone greater than 4mm
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Which form of metabolism (from chapter 5 in your lecture book) utilizes nitrate salt as a final electron acceptor?
Anaerobic respiration
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Is nitrate an oxidized or a reduced salt?
Nitrate is an oxidized salt
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What is the molecular formula of nitrate?
NO3-
