Which phase of the microbial growth curve would an obligate anaerobe most likely exhibit when grown in the presence of oxygen in a closed system?

• A. Lag phase
• B. Death phase
• C. Log (exponential) phase
• D. Stationary phase

Answer: (B)

Verified step by step guidance

1. Understand the characteristics of an obligate anaerobe: these microbes cannot survive in the presence of oxygen because it is toxic to them.
2. Recall the phases of the microbial growth curve: Lag phase (adaptation), Log phase (rapid growth), Stationary phase (growth rate equals death rate), and Death phase (decline in viable cells).
3. Consider what happens when an obligate anaerobe is exposed to oxygen in a closed system: since oxygen is harmful, the cells will not grow or adapt normally.
4. Analyze the expected phase: the cells will likely not enter the Log phase because they cannot multiply in oxygen; instead, they will begin to die off due to oxygen toxicity.
5. Conclude that the microbial population will most likely be in the Death phase, where the number of dying cells exceeds the number of new cells formed.