Questions and Answers
List five groupings of microorganisms according to their oxygen tolerance.
- Obligate aerobes, 2. Facultative anaerobes, 3. Obligate anaerobes, 4. Aerotolerant anaerobes, 5. Microaerophiles.
What are capnophiles?
Capnophiles are microaerophiles that can only survive if carbon dioxide levels are elevated.
Describe the procedure for preparing agar shake cultures.
Inoculate with a loop then gently roll to spread.
How does a GasPak create anaerobic conditions?
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Why are stab cultures heated or boiled?
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What is the purpose of catalase in bacterial metabolism?
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Anaerobes have superoxide dismutase to protect them from oxygen.
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Why are tubed media boiled prior to inoculation?
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Name at least one bacterial genus that tolerates oxygen but does not produce catalase.
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Why is it important to time how long it takes for the candle in a candle jar to go out?
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How does adding a small amount of agar to Thioglycollate Medium help?
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What does the term 'fastidious' refer to in bacterial culturing?
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Why does moisture accumulate in the candle jar after it has been sealed?
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Study Notes
Oxygen Tolerance Groupings
- Obligate aerobes: Require oxygen for survival; cannot grow without it.
- Facultative anaerobes: Prefer oxygen but can survive without it; capable of both aerobic and anaerobic respiration.
- Obligate anaerobes: Cannot tolerate oxygen; oxygen is toxic to them.
- Aerotolerant anaerobes: Oxygen is not toxic, but they do not utilize it for growth.
- Microaerophiles: Require low levels of oxygen; high concentrations are toxic.
Characteristics of Capnophiles
- Capnophiles are microaerophilic organisms that thrive in environments with elevated carbon dioxide levels.
Growth Methods for Various Oxygen Tolerances
- Agar shake cultures: Inoculate using a loop and roll gently to distribute.
- Stab cultures: Inoculate with a needle into the agar deep.
- Fluid Thioglycollate Medium: Inoculate with a loop; enables growth of various oxygen-dependent microbes.
- Candle jars: Inoculated plates are sectioned and placed in a jar with a lit candle; the candle consumes oxygen, creating a microaerophilic environment.
- Gas Packs: Sealed bags or jars containing inoculated plates react with gas packs to create anaerobic conditions.
Creating Anaerobic Environments
- Stab cultures: Heating drives out oxygen; older tubes may need reheating to remove trapped oxygen.
- Fluid Thioglycollate Medium: Contains sodium thioglycolate to consume oxygen and create varied oxygen concentrations.
- Gas packs: The indicator changes color based on oxygen presence; chemical reactions produce gases to create anaerobic environments.
Redox Potential Assessment
- Gas Pak: Produces anaerobic conditions for culturing anaerobes. Methylene blue indicator shows the presence of oxygen, turning blue when oxygen is detected.
- Fluid Thioglycollate Medium: Consumes oxygen, allowing obligate anaerobes to grow; redox indicators change color based on oxygen levels.
Enzymatic Protection Against Oxygen
- Catalase: Converts hydrogen peroxide into water and oxygen, protecting cells from oxidative damage.
- Superoxide dismutase: Breaks down superoxide radicals into hydrogen peroxide, functioning in defense against oxygen toxicity.
Anaerobic Sensitivity to Oxygen
- Anaerobes lack superoxide dismutase, making them vulnerable to oxidative stress and lethal effects of oxygen.
Importance of Boiling Tubed Media
- Boiling media before inoculation removes dissolved air and oxygen, crucial for the survival of anaerobic organisms.
Oxygen-Tolerating Bacteria
- Streptococcus: Example of a genus that tolerates oxygen without producing catalase; relies on other mechanisms for protection.
Timing in Candle Jar Use
- Timing the candle's extinguishing ensures sufficient buildup of carbon dioxide and depletion of oxygen for anaerobic conditions.
Agar in Thioglycollate Medium
- A small amount of agar thickens the medium, slowing oxygen diffusion into the broth, beneficial for anaerobic growth.
Definition of Fastidious Bacteria
- Fastidious bacteria have specific growth requirements including nutrients, temperature, pH, salinity, and oxygen levels.
Moisture in Candle Jars
- Moisture accumulation is due to the reaction between hydrogen and free oxygen catalyzed by palladium, leading to anaerobic conditions as free oxygen is consumed.
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Description
Explore the five different groupings of microorganisms based on their oxygen tolerances in this informative quiz. Learn the unique characteristics of obligate aerobes, facultative anaerobes, obligate anaerobes, aerotolerant anaerobes, and microaerophiles. Test your knowledge and understanding of microbial oxygen requirements.
