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Renin Angiotensin Mechanism.

Bacterial Growth Curve.

 

Introduction:

  • Bacteria are a prokaryotic organism mostly grow by asexual reproduction like fission.

  • When grown in a culture bacterias show a predictable pattern of growth called “Growth Curve”.

  • The growth curve is a graphical representation of “No. of living bacterial cells against time”.

  • A bacterial population's generation time, or time it takes for a population to double, varies between species and depends on many factors.

  • Bacterial growth cycles in a growth curve consist of four phases: 

    • Lag Phase, 

    • Exponential (log) Phase, 

    • Stationary Phase, and 

    • Death or Decline Phase.

  1. Lag Phase:

  • This first phase is characterized by cellular activity but not growth. 

  • The inoculum is placed in a nutrient rich medium that allows the cells to synthesize proteins and other molecules necessary for replication. 

  • These cells increase in size, but no cell division occurs in the phase.

  • Lag Phase: Increase cell sizes but no cell replication.

  1. Log Phase:

  • Also called ”Exponential Phase”.

  • After the lag phase, bacterial cells enter the exponential or log phase.

  • Metabolic activity is high as DNA, RNA, cell wall components, and other substances necessary for growth are generated for division.

  • Cells are smaller in size and multiplying rapidly. 

  • It is in this growth phase that antibiotics and disinfectants are most effective as these substances typically target bacteria cell walls or the protein synthesis processes of DNA transcription and RNA translation.

  • Log Phase: Smaller sized cells with high metabolic activity, shows rapid cell multiplication.

  1. Stationary Phase:

  • Eventually, the population growth happened in the log phase begins to decline as the available nutrients become depleted and waste products start to accumulate. 

  • Bacterial cell growth reaches a plateau, or stationary phase, where the number of dividing cells equal the number of dying cells. 

  • This results in no overall population growth. 

  • Under the less favorable conditions, competition for nutrients increases and the cells become less metabolically active. 

  • Spore forming bacteria produce endospores in this phase and pathogenic bacteria begin to generate substances (virulence factors) that help them survive harsh conditions and consequently cause disease.

  • Stationary Phase: Cells are metabolically inactive, no overall growth, formation of endospores and virulence factors.

  1. Death Phase:

  • Also called phase of Decline.

  • As nutrients become less available and waste products increase, the number of dying cells continues to rise. 

  • In the death phase, the number of living cells decreases exponentially and population growth experiences a sharp decline. 

  • As dying cells lyse or break open, they spill their contents into the environment making these nutrients available to other bacteria. 

  • This helps spore producing bacteria to survive long enough for spore production. 

  • Spores are able to survive the harsh conditions of the death phase and become growing bacteria when placed in an environment that supports life.

  • Death Phase: No. of dying cells further increase, spore formation.

Bacterial Growth Curve Key Points to remember.

  • Graphical representation of bacterial growth “No. of living bacterial cells against time”.

  • Four Stages:

  • Lag Phase: Increase cell sizes but no cell replication.

  • Log Phase: Smaller sized cells with high metabolic activity, shows rapid cell multiplication.

  • Stationary Phase: Cells are metabolically inactive, no overall growth, formation of endospores and virulence factors.

  • Death Phase: No. of dying cells further increase, spore formation.
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