During which growth phase are Gram-positive bacteria most susceptible to penicillin?

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

Answer: (D)

Verified step by step guidance

1. Understand the bacterial growth phases: Lag phase (adaptation period), Log (exponential) phase (rapid cell division), Stationary phase (growth rate slows due to nutrient depletion), and Death (decline) phase (cells die).
2. Recall that penicillin targets the synthesis of peptidoglycan, a key component of the bacterial cell wall, which is actively produced during cell division.
3. Identify that during the Log (exponential) phase, bacteria are actively dividing and synthesizing new cell walls, making them more vulnerable to antibiotics like penicillin.
4. Recognize that in the Lag phase, bacteria are metabolically active but not dividing, so penicillin is less effective; in the Stationary and Death phases, cell division slows or stops, reducing penicillin's impact.
5. Conclude that Gram-positive bacteria are most susceptible to penicillin during the Log (exponential) phase because this is when cell wall synthesis is at its peak.