Biochemical Testing for Microbial Identification - Methyl Red, Voges- Proskauer, and Catalase Testing Flashcards
Identifies metabolic properties of microbes
biochemical testing
Enzyme that mediates the breakdown of hydrogen peroxide
Catalase
Anaerobic metabolism that produces acids, alcohol, and gases
Mixed acid fermentation
Anaerobic metabolism that produces acetoin
Butanediol fermentation
Metabolic process resulting in oxygen and peroxide by-products
Aerobic respiration
True/False: Methyl red is associated with low pH and mixed acid fermentation.
True
Biochemical tests are designed to identify _____ properties of microbes.
Metabolic
Mixed-acid fermentation produces _____.
acetic acid, ethanol, and hydrogen gas
Methyl red is a pH indicator that turns red in _____ conditions.
acidic
True/False: Fermentation occurs when carbohydrates are metabolized anaerobically.
True
T/F MR-VP broth contains nutrients and buffers.
T
T/F: All aerobic microbes lack the enzyme catalase.
F
T/F: Biochemical tests provide more generalized information than morphological observations.
F
Biochemical tests are designed to identify _____ properties of microbes.
a.) morphologic
b.) metabolic
c.) motility
d.) All of the above
b.) Metabolic
Blank is the conversion of sugars to acids, gases, and/or alcohol.
Fermentation
What does the methyl red test for?
The methyl red test is designed to identify microbes that perform mixed-acid fermentation.
What is mixed-acid fermentation?
Mixed-acid fermentation is an anaerobic metabolic process that produces lactic acid, acetic acid, ethanol, carbon dioxide and hydrogen gas.
What pH does the pH indicator methyl red turn red?
Acidic pHs between 4.4 and 6.0.
Blank contains 0.5% glucose, peptones and buffers.
MR-VP broths
What color do cultures that are not mixed fermentation turn when a methyl red test is conducted?
Cultures demonstrating mixed-acid fermentation turn red when methyl red is added to the broth because the mixed-acid fermentation creates acidic by-products that do not neutralize in the buffered solution. Cultures that do not undergo mixed-acid fermentation turn yellow when methyl red is added, indicating a negative test result.
Mixed-acid fermentation produces _____.
a.) acetic acid
b.) ethanol
c.) hydrogen gas
d.) All of the above
d.) All of the above
Methyl red is a pH indicator that turns red in _____ conditions.
acidic
What does Voges-Proskauer test do?
The Voges-Proskauer test is designed to identify microbes that ferment glucose via the butanediol pathway.
T/F: Butanediol fermentation produces weaker acids than mixed-acid fermentation.
True
Which enzyme neutralizes the harmful effects of hydrogen peroxide?
Catalase
T/F: Anaerobic microbes typically have catalase.
F
What does catalase mediates breakdown hydrogen peroxide into?
O2 and H2O
What occurs when hydrogen peroxide is added to a colony of catalase-positive microbes (aerobic microbes)?
oxygen bubbles rapidly form.
Catalase neutralizes the harmful effects of _____.
Hydrogen peroxide
Which of the following is Voges- Proskauer associated with?
a.) Barritt’s reagents
b.) Butanediol fermentation
c.) Mixed- acid fermentation
d.) Both a and b
d
What color will a positive Voges-Proskauer test turn?
Red
Why are biochemical tests used to identify microbes?
Biochemical tests are designed to identify metabolic properties of an organism to lead to ambiguous identification of organisms.
What is mixed-acid fermentation? How is methyl red used to determine if a microbe has undergone mixed-acid fermentation?
Mixed-acid fermentation involves the conversion of a six-carbon sugar into a complex and variable mixture of acids. After methyl red is added to the color of the microbe, it will turn red if it has undergone mixed-acid fermentation and it will have a positive result.
Why are the methyl red and Voges-Proskauer tests often performed together?
The methyl red and Voges-Proskauer test are performed together to differentiate bacteria within the Enterobacteriaceae family.
Is E. coli positive or negative for the methyl red test?
Positive, Since E. coli had a positive methyl red test, this indicates that E. coli is able to convert to pyruvate then to mixed organic acids.
Is S. Epi positive or negative for the methyl red test?
S. epidermidis was negative for the methyl red test, it doesn’t have the ability to maintain and produce acid end products from glucose fermentation. Since S. epidermidis was negative for the methyl red test, less acid is produced from the fermentation of glucose.
Is E. coli positive or negative for the vogues-proskauer test, what does the result mean?
In the Vogues-Proskauer test E. coli was negative therefore it cannot convert glucose to acetoin.
Is S. epi positive or negative for the Vogues-Proskauer test? what does it mean?
The S. epidermidis is expected to have a positive result for the Vogues-Proskauer test, therefore, it is able to metabolically convert glucose to acetoin
What kind of fermentation does E. coli use?
E. Coli tested positive for the methyl red test, it uses mixed-acid fermentation.
What kind of fermentation does S. epi use?
Since S. epidermidis is positive for the Vogues-Proskauer test, it use butanediol fermentation.
What were the catalase test results for E. coli?
Positive, bubbles appeared on the slide after the addition of one drop of hydrogen peroxide.
What were the catalase test results for S. epi?
Negative, no bubbles formed
What is catalase? What types of microbes are more likely to produce catalase?
Catalase is an enzyme that catalyzes the reaction that decomposed hydrogen peroxide to water and oxygen. [1] Aerobic microbes are more likely to produce catalase, this is evidenced by rapidly forming oxygen bubbles after the addition of hydrogen peroxide.
what can you conclude about the metabolism of E. coli and S. epidermidis? Catalase test
Since E. coli was positive for the catalase test, E. coli does contain the catalase enzyme used to convert hydrogen peroxide to water and oxygen. Since S. epidermidis was negative for this test, the catalase enzyme is not found in S. epidermidis and therefore S. epidermidis cannot be used to convert hydrogen peroxide to water and oxygen gas.
The _____ is a biochemical test used to determine the identity of an unknown microbe.
a.) Methyl red test
b.) Voges - Proskauer test
c.) Catalase test
d.) All of the above
d
T/F: Fermentation occurs when carbohydrates are broken down aerobically.
F
The methyl red test detects a microbe’s ability to _____.
perform mixed - acid fermentation
The products of mixed-acid fermentation _____ the pH of buffered media
lower
Butanediol fermentation produces _____ acids compared to mixed-acid fermentation.
a.) stronger
b.) weaker
c.) identical
d.) none of the above
b. weaker
T/F: The methyl red and Voges-Proskauer tests are typically performed together to differentiate bacteria within the family Enterobacteriaceae.
True
Oxygen ions and _____ are metabolites of aerobic respiration that can damage cell structures.
a.) alcohols
b.) peroxides
c.) mixed acids
d.) None of the above
b.) peroxides
_____ broth is used to culture microbes for the methyl red and Voges-Proskauer tests
MR-VP
Red-stained media is a _____ result for the methyl red test.
positive
Positive Voges-Proskauer test appears as _____.
A red layer atop yellow media
_____ is a positive result for catalase testing.
Bubbling peroxide
A microbe produced positive methyl red results and negative Voges-Proskauer results. It can be concluded that the microbe _____.
a.) respires aerobically
b.) produces mixed acids but does not use the butanediol pathway
c.) uses the butanediol pathway but does not produce mixed acids
d.) None of the above
b.) produces mixed acids but does not use the butanediol pathway
