Microbial oxygen relationships — The term “obligate anaerobe” refers to an organism that…

Introduction / Context:
Oxygen requirements are a foundational way to classify microorganisms and predict where they can survive (tissues, foods, environments). Categories include obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes, and microaerophiles. Correct definitions drive proper culturing methods and infection control strategies.

Given Data / Assumptions:

• “Obligate” implies a strict requirement or strict exclusion.
• Reactive oxygen species (ROS) such as superoxide and hydrogen peroxide can be lethal without detoxifying enzymes.
• We contrast true oxygen lethality with mere preference or tolerance.

Concept / Approach:
Obligate anaerobes lack adequate ROS-detoxifying systems (e.g., catalase, superoxide dismutase) and therefore cannot survive exposure to atmospheric oxygen. Oxygen damages cellular components and halts essential metabolic pathways. This differs from aerotolerant anaerobes (tolerate oxygen but do not use it), facultative anaerobes (can switch to aerobic respiration when oxygen is present), and microaerophiles (require reduced oxygen tension).

Step-by-Step Solution:

Verification / Alternative check:
Clinical handling of strict anaerobes (e.g., Clostridium, Bacteroides) uses anaerobic chambers or jars to avoid oxygen exposure, reinforcing the lethal effect of oxygen on these microbes.

Why Other Options Are Wrong:

• Doesn’t use but tolerates oxygen: describes aerotolerant anaerobes.
• Uses oxygen or grows without it: describes facultative anaerobes.
• Prefers no oxygen: suggests microaerophiles or facultatives with preference, not lethality.

Common Pitfalls:
Confusing “tolerance” with “requirement”; “obligate” emphasizes strict exclusion of oxygen for survival.

Final Answer:
is killed by oxygen