Bacterial Growth Curve

Overview

• The bacterial growth curve consists of four phases:
  1. Lag Phase
  2. Log Phase
  3. Stationary Phase
  4. Death Phase

Lag Phase

• Characteristics: Appears as a horizontal line on a graph.
• Population Change: No increase in the number of living bacterial cells.
• Activities:
  • Bacteria are preparing for growth.
  • Synthesis of enzymes and metabolic products.
• Analogies:
  • Building a factory before production.
  • Interphase during cell cycle in mitosis.

Log Phase

• Also known as the exponential phase.
• Characteristics:
  • Exponential or logarithmic growth.
  • The generation time is constant.
  • Example: E. coli has a generation time of ~20 minutes.
• Population Change:
  • Rapid doubling of the population.
  • Potential for enormous growth if unchecked (e.g., in 25.5 hours, a single cell could weigh 80,000 tons).
• Susceptibility:
  • Bacteria are most susceptible to treatments (e.g., antibiotics) during this phase.

Stationary Phase

• Also referred to as the plateau phase.
• Characteristics: Births equal deaths.
• Population Change:
  • No net increase in population.
  • Cells continue to divide, but death rates equal birth rates.
• Limitations:
  • Lack of space and food.
  • Accumulation of toxic waste products.
  • Environmental changes such as pH shifts.

Death Phase

• Also known as the decline phase.
• Characteristics:
  • Logarithmic decline in population.
  • Death rate surpasses birth rate.
• Population Change:
  • Rapid decrease in population size.
  • Can lead to near-complete disappearance of the population.
  • Some organisms may persist for years.

Additional Insights

• During the log phase, treatments that inhibit cell wall formation (e.g., penicillin) or protein synthesis have the most impact.

Conclusion

• Understanding the bacterial growth curve is crucial for determining when bacteria are most vulnerable to treatments.
• The phases indicate different rates of growth and population changes over time.