Questions and Answers
What does the Glucose Fermentation test detect?
A fermentation reaction
Why is it necessary to record the results of carbohydrate fermentation tests no later than 48 hours after inoculation?
The carbohydrate supply is exhausted and bacteria begin growing oxidatively.
A positive reaction for carbohydrate fermentation is indicated by the production of acidic wastes, which turn the phenol red pH indicator _____.
yellow
Which of the following organisms are capable of lactose fermentation with the production of acid?
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What alternative nutrient source may Pseudomonas aeruginosa have used to produce energy in the absence of carbohydrates?
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The pH indicator used when bacteria break down the citrate in Simmons citrate agar is _____
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What indicates a positive test for acetoin production in the methyl red Voges-Proskauer test?
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Which of the following is an INCORRECT statement regarding carbohydrate fermentation testing?
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Fermentation occurs only in the absence of O2.
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What color is phenol red in the presence of acid?
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The indicator in fermentation tubes is __________.
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Bacteria that ferment can metabolize all carbohydrates in the same manner.
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All bacteria have the ability to ferment any sugar available.
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What does a yellow broth with a trapped bubble indicate after 24 hours of incubation?
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Fermentation of the sugars in a Durham tube will always result in gas production.
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You have a phenol red lactose Durham tube and a phenol red sucrose Durham tube, both yellow, with a gas bubble in the lactose tube but no bubble in the sucrose tube. Which bacterium did you inoculate into both Durham tubes?
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The only carbohydrate in a phenol red lactose broth tube is the sugar lactose.
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To inoculate a Durham tube you would need to use __________.
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You should inoculate a phenol red dextrose tube on Friday and observe the results when you return on Monday.
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Study Notes
Glucose Fermentation Test
- Detects fermentation reactions within a culture medium using an inoculating loop.
- Contains phenol red, which turns yellow in acidic environments.
- Prior to inoculation, the mouth of the tube should be flamed and capped immediately after.
Timing of Results
- Record carbohydrate fermentation test results no later than 48 hours to avoid nutrient exhaustion.
- Prolonged incubation changes the pH indicator due to bacterial oxidation of peptones.
Indicators of Reactions
- A positive fermentation reaction produces acidic waste, turning phenol red yellow.
- The pH indicator for citrate breakdown in Simmons citrate agar is bromthymol blue, which indicates alkalization due to ammonia release.
Bacteria and Fermentation
- Organisms capable of lactose fermentation with acid production include Staphylococcus aureus and Escherichia coli.
- Pseudomonas aeruginosa, unable to utilize carbohydrates, may derive energy from amino acids.
Testing and Analysis
- Methyl red Voges-Proskauer test shows red color after adding potassium hydroxide and alpha-naphthol, indicating acetoin production.
- Incorrect statement: A gas bubble in the Durham tube indicates acetic acid production—this is not true.
Misconceptions
- Fermentation can occur in both aerobic and anaerobic conditions.
- Not all bacteria can ferment all carbohydrates; fermentation capabilities vary between species.
- Phenol red does not turn yellow in the presence of bacteria alone; it indicates acid production from fermentation.
Test Results Interpretation
- A yellow broth with a trapped bubble in a Durham tube indicates successful fermentation of the sugar source with CO2 production.
- If the Durham tubes remain red with trapped bubbles but no growth, it may be due to agitation during handling.
Fermentation Characteristics
- Fermentation of sugars may not always lead to gas production.
- A phenol red lactose Durham tube and a sucrose tube can both show results indicative of specific bacterial fermentation capabilities.
Practical Aspects of Inoculation
- Use any sterile instrument to transfer a bacterial suspension into a Durham tube.
- Inoculating a phenol red dextrose tube on a Friday and expecting results by Monday is not advisable.
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Description
Explore the key concepts of carbohydrate fermentation through this flashcard quiz. Review important definitions and procedures related to fermentation tests, including the role of phenol red and proper inoculation techniques. Perfect for reinforcing your knowledge in microbiology.
