Bacterial Growth Curve
- When a broth culture is inoculated with a small bacterial inoculum, the population size of the bacteria increases.
- The bacterial growth curve shows the following four distinct phases.
- Lag phase, Log phase, Stationary phase, Decline phase.
- After a liquid culture broth is inoculated, the multiplication of bacteria does not start immediately. It takes some time to multiply.
- The time between inoculation and beginning of multiplication is known as lag phase.
- In this phase, the inoculated bacteria accommodate to the environment, switch on various enzymes, and adjust to the environmental temperature and atmospheric conditions.
- During this phase, there is an increase in size of bacteria but no increase in number of bacterial cells.
- The cells are active metabolically.
- The duration of the lag phase varies with the bacterial species, nature of culture medium, incubation temperature, etc. It may vary from 1 hour to several days.
- This phase is characterized by rapid exponential cell growth (i.e., 1 to 2 to 4 to 8 and so on).
- The bacterial population doubles during every generation.
- They multiply at their maximum rate.
- The bacterial cells are small and uniformly stained. The microbes are sensitive to adverse conditions, such as antibiotics and other antimicrobial agents.
- After log phase, the bacterial growth almost stops completely due to lack of essential nutrients, lack of water oxygen, change in pH of the medium, etc. And accumulation of their own toxic metabolic wastes.
- Death rate of bacteria exceeds the rate of replication of bacteria.
- Endospores start forming during this stage.
- Many bacteria start producing exotoxins.
- During this phase, the bacterial population declines due to death of cells.
The decline phase starts due to:
(a) accumulation of toxic products and autolytic enzymes.
(b) exhaustion of nutrients.
- Involution forms are common in this stage.