During which growth phase will gram-positive bacteria be most susceptible to penicillin?
lag phase
log phase
stationary phase
they are not sensitive to penicillin
The correct answer and explanation is :
The correct answer is log phase.
Penicillin, a beta-lactam antibiotic, works by inhibiting the synthesis of the bacterial cell wall. This is particularly effective in bacteria that are actively growing and dividing, as they are constantly synthesizing new cell walls to accommodate their growth. The log phase, also known as the exponential phase, is the phase of bacterial growth where the bacteria are multiplying at the fastest rate. During this phase, the cells are highly metabolically active, and cell wall synthesis is occurring rapidly to support the division of the bacteria.
Lag Phase: In this phase, bacteria are adjusting to their environment, and metabolic activity is high but they are not dividing yet. Penicillin would have limited effect because the bacteria aren’t actively synthesizing new cell walls at this stage.
Stationary Phase: This phase is characterized by a balance between the rate of bacterial cell growth and the rate of bacterial cell death. Although some bacterial cell division continues, overall growth slows down. Since the bacteria are not dividing as quickly or producing as much new cell wall material, they are less susceptible to penicillin. Penicillin works best on dividing cells, so its effectiveness diminishes during this phase.
Why the Log Phase is Most Susceptible: Penicillin targets enzymes involved in cell wall synthesis, which are active during bacterial growth. During the log phase, as bacteria are actively dividing and creating new cell walls, penicillin can effectively disrupt this process, leading to cell lysis (rupture) and ultimately bacterial death. In contrast, during the lag and stationary phases, where cell division is slower or halted, penicillin has less opportunity to interfere with cell wall synthesis, making the bacteria less susceptible to the antibiotic.
In summary, gram-positive bacteria are most susceptible to penicillin during the log phase, when they are rapidly dividing and synthesizing cell walls.