Microorganisms Oxygen Tolerance Quiz

Study Notes

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.

Capnophiles are microaerophilic organisms that thrive in environments with elevated carbon dioxide levels.

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.

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.

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.

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.

Anaerobes lack superoxide dismutase, making them vulnerable to oxidative stress and lethal effects of oxygen.

Boiling media before inoculation removes dissolved air and oxygen, crucial for the survival of anaerobic organisms.

Streptococcus: Example of a genus that tolerates oxygen without producing catalase; relies on other mechanisms for protection.

Timing the candle's extinguishing ensures sufficient buildup of carbon dioxide and depletion of oxygen for anaerobic conditions.

A small amount of agar thickens the medium, slowing oxygen diffusion into the broth, beneficial for anaerobic growth.

Fastidious bacteria have specific growth requirements including nutrients, temperature, pH, salinity, and oxygen levels.

Moisture accumulation is due to the reaction between hydrogen and free oxygen catalyzed by palladium, leading to anaerobic conditions as free oxygen is consumed.