Simple Pharmanotes: 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.

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.

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.

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.

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.