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.
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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-
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What is the is reduction process showing nitrate being reduced to ammonia?
- NO3- —> NO2- —>N2O(g) —>N2 —> NH3
- Nitrate reduced to Nitrite (red color change), Nitrite reduced to Nitrous oxide, Nitrous oxide reduced to nitrogen gas (bubbles form in durham tube), Nitrogen gas reduced to ammonia.
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In the anaerobic respiration / nitrate test, which reduced products are gases?
Nitric oxide (NO) and nitrous oxide (N2O) are gases.
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Which color is produced by a positive nitrite test?
Red
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Is a positive nitrite test a positive or negative result for nitrate reduction?
A positive nitrite test indicates nitrate reduction.
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What is the function of a Durham tube?
It traps gas in the nitrate broth.
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Is the presence of bubbles in the Durham tube positive or negative for nitrate reduction?
Positive; bubbles indicate gas production.
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What would the results look like for an organism that did not use the nitrate?
No color change, no gas production
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Gelatin is what type of biological molecule?
Protein
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What is the name of the enzyme that hydrolyzes gelatin?
Protease
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How did we inoculate the gelatin agar so that it could be incubated?
Using needle
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If we were to analyze the tubes for gelatin hydrolysis directly after removing the cultures from the incubator, our results would be incorrect. What do we need to do before analyzing the results of our hydrolysis test?
Chill the tubes to solidify the gel
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Briefly describe the appearance of a tube that is positive for gelatin hydrolysis.
The medium remains liquid after chilling.
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What are the 2 Vogel Johnson Agar test are and the results of these tests?
- Testing for Coagulase
- Testing for mannitol fermentation
Positive result for coagulase = black colonies
Positive result for mannitol fermentation = yellow zones around colonies
Negative result = no black or yellow
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How are black colonies formed as a positive result from the Vogel-Johnson agar test?
Tellurite gets reduced into bellurium.
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What concentration of NaCl is used in our hypertonic broth?
6.5% saline solution
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Which pH indicator is present in the saline broth?
NaCl test
Bromocrosal Purple
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What color is the broth before it is inoculated in the NaCl test?
NaCl saline test
Purple
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How does bacterial growth affect the pH of the saline broth?
Decreases pH making it more acidic
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What is expected with a positive test result in the NaCl saline test?
- Broth becomes cloudy
- Broth changes to yellow-brown
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What does BEA stand for?
Bile Esculin Agar
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Which two ingredients in a BEA plate act to select against the growth of most microbes?
1.) Bile
2.) Azide
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What is the substrate in the BEA plate?
Esculin
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What are the two products of degradation? Which of these products reacts with iron ions?
BEA test
Two products of degradation:
1.) Glucose
2.) Esculetin
Esculetin reacts with iron ions
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What color is produced by a positive test result?
BEA test
Black splotches
