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What is the primary function of catalase in bacteria?
What is the primary function of catalase in bacteria?
Which of the following organisms is most likely to test positive for coagulase?
Which of the following organisms is most likely to test positive for coagulase?
In which test is free coagulase detected?
In which test is free coagulase detected?
What precaution should be taken when performing the catalase test?
What precaution should be taken when performing the catalase test?
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What do differential media like MacConkey agar help differentiate?
What do differential media like MacConkey agar help differentiate?
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What is the main use of the oxidase test?
What is the main use of the oxidase test?
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Which type of coagulase test is used to screen isolates of Staphylococcus aureus?
Which type of coagulase test is used to screen isolates of Staphylococcus aureus?
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Why is it important to process all samples in accordance with the SOP designed for the test?
Why is it important to process all samples in accordance with the SOP designed for the test?
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What is the significance of the bound coagulase in the clumping factor test?
What is the significance of the bound coagulase in the clumping factor test?
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What color change indicates a positive result in the oxidase test?
What color change indicates a positive result in the oxidase test?
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During the urease test, what is the role of the enzyme urease?
During the urease test, what is the role of the enzyme urease?
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API 20 E is primarily used for identifying which type of organisms?
API 20 E is primarily used for identifying which type of organisms?
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What must be observed during the oxidase test to confirm results?
What must be observed during the oxidase test to confirm results?
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In the urease test, what does a rapid color change to pink within 24 hours indicate?
In the urease test, what does a rapid color change to pink within 24 hours indicate?
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What role does phenol red play in the urease test?
What role does phenol red play in the urease test?
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Which of the following is a precaution for performing the oxidase test?
Which of the following is a precaution for performing the oxidase test?
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Which characteristic does the API test system focus on during bacterial identification?
Which characteristic does the API test system focus on during bacterial identification?
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What is the initial color of the urea medium at a neutral pH?
What is the initial color of the urea medium at a neutral pH?
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What does a positive result indicate in this observation?
What does a positive result indicate in this observation?
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Which of the following samples can be used as a control in the experiment?
Which of the following samples can be used as a control in the experiment?
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Which organism is identified through the lactose fermentation in the flowchart?
Which organism is identified through the lactose fermentation in the flowchart?
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What characteristic distinguishes aerobic from anaerobic bacilli in the flowchart?
What characteristic distinguishes aerobic from anaerobic bacilli in the flowchart?
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Which organism is incorrectly categorized as an anaerobic bacilli?
Which organism is incorrectly categorized as an anaerobic bacilli?
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What indicates a positive result in the coagulation test with mammalian plasma?
What indicates a positive result in the coagulation test with mammalian plasma?
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Which organism serves as the positive control in the oxidase test?
Which organism serves as the positive control in the oxidase test?
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In the dry filter paper method of the oxidase test, what does a positive reaction indicate?
In the dry filter paper method of the oxidase test, what does a positive reaction indicate?
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What is the incubation temperature for the urease test procedure?
What is the incubation temperature for the urease test procedure?
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Which statement is correct regarding the results of the coagulation test?
Which statement is correct regarding the results of the coagulation test?
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What should be ignored in the oxidase test interpretation?
What should be ignored in the oxidase test interpretation?
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What is the main purpose of using Christensen's urea agar medium?
What is the main purpose of using Christensen's urea agar medium?
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What indicates a negative result in the oxidase test?
What indicates a negative result in the oxidase test?
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Which organism serves as the negative control in the urease test?
Which organism serves as the negative control in the urease test?
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In the coagulation test, when should the plasma tube be examined for results?
In the coagulation test, when should the plasma tube be examined for results?
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What does a positive catalase test indicate?
What does a positive catalase test indicate?
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Which type of control organism is used in the catalase test?
Which type of control organism is used in the catalase test?
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What indicates a negative result in the slide coagulase test?
What indicates a negative result in the slide coagulase test?
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What action should be taken if the reagent used in the catalase test is expired?
What action should be taken if the reagent used in the catalase test is expired?
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What is the main principle behind the tube coagulase test?
What is the main principle behind the tube coagulase test?
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In a coagulase test, which organism is typically a negative control?
In a coagulase test, which organism is typically a negative control?
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What should be checked before using the API 20 E strip?
What should be checked before using the API 20 E strip?
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What constitutes a positive result in the tube coagulase test?
What constitutes a positive result in the tube coagulase test?
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What is the correct method for performing the catalase test?
What is the correct method for performing the catalase test?
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Which equipment is essential for performing both the catalase and coagulase tests?
Which equipment is essential for performing both the catalase and coagulase tests?
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Study Notes
Basic Microbiology - Practical No. 6
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Intended Learning Objectives (ILOs):
- Students will be introduced to selective and differential media and learn to define both types.
- Students will differentiate between lactose and non-lactose fermenting bacteria on MacConkey agar.
- Students will understand the significance of catalase and coagulase tests, and their principles.
- Students will perform and interpret catalase and coagulase tests.
- Students will understand the importance of Oxidase and Urease tests, and their principles.
- Students will perform and interpret Oxidase and Urease tests.
- Students will be introduced to the API-20E test and learn to interpret its results.
Precautions
- Wear appropriate personal protective equipment (PPE) for the lab procedure.
- All specimens should be treated as infectious.
- Follow all standard operating procedures (SOPs) designed for each test.
- Record results immediately.
Catalase
- Catalase is an enzyme that breaks down hydrogen peroxide (H₂O₂) into oxygen (O₂) and water (H₂O).
- Most aerobic and facultative anaerobic bacteria have catalase activity.
- This test helps identify unknown bacteria.
- Do not use metal instruments with H₂O₂ or take colonies from blood agar, as this may give false positive results due to metal degradation.
Coagulase
- Staphylococcus aureus produces coagulase, which clots plasma using two mechanisms (free and bound).
- This enzyme is useful in differentiating S. aureus from other coagulase-negative staphylococci.
Oxidase
- This test identifies organisms that produce cytochrome c oxidase.
- A chromogenic reducing agent in the reagent changes colour when oxidized.
- If the organism produces cytochrome oxidase, the reagent turns blue or purple within 15 seconds.
Urease
- Urea agar (developed by Christensen in 1946) is used to differentiate enteric bacilli.
- The urease test determines the ability of an organism to split urea via the production of the enzyme urease.
- Hydrolysis of urea produces ammonia and CO₂.
- Formation of ammonia leads to alkalinization, which is detected by phenol red colour change.
- Weakly positive organisms may take several days to produce a colour change from light orange to magenta.
API 20E Test
- API 20E is a multi-test system useful for identifying bacteria (e.g. enteric bacteria, non-fastidious Gram-negative rods).
- It employs 20 miniaturized biochemical tests.
- Time, cost, and space are key factors in clinical laboratory usage of this system.
Catalase Test (Procedure)
- Using a clean microscope slide, add a drop of H₂O₂.
- Use a loop to pick up bacteria from a solid medium and place it in the drop.
- Observation: Look for rapid gas bubble production (positive) or no gas bubbles (negative).
Coagulase Test (Procedure)
- Use a slide and inoculate it.
- Place one drop of citrated mammalian plasma on the slide and mix.
- Observe immediate clumping; this indicates a positive result.
- Alternatively, use a tube method for this test to distinguish between free and bound coagulase.
Oxidase Test (Procedure)
- Use sterile filter paper and add oxides reagent.
- Then add bacterial colonies to the filter paper
- Observe for a colour change to purple within 10-30 seconds.
Urease Test (Procedure)
- Inoculate a urea slant with the test organism.
- Incubate at the appropriate temperature for 24-72 hrs and observe for colour change to pink/red.
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Description
This quiz focuses on practical skills in microbiology, specifically selective and differential media, and tests like catalase, coagulase, oxidase, and urease. Students will learn to differentiate between bacteria and interpret the results of various lab tests. The emphasis is on the applications of these tests in understanding bacterial properties.
