Principle Microbiology

Bacterial Growth curve

Bacteria, when transferred from one medium to another, shows characterstic growth curve.
It shows four distinct phase of growth.
Lag phase
Log or exponential phase
Stationary phase
Decline or death phase

Lag phase :- When the bacteria are transferred from one medium to another they do not show sudden growth as they may be depleted of energy. The nutrients may be different in two media. Organisms synthesize new enzymes to utilize new nutrients. Organisms increase in size but show no change in number.
Log phase :- In this phase bacteria divide exponentially. The graph shows curve which means not all the bacteria multiply simultaneously. After some time period the no. of division fall down.
Stationary phase :- In this phase bacterial population does not change with time - No. of bacteria born are same as no. of bacteria died.
Decline phase :- In this phase bacteria die exponentially. Bacterial population fall down as inverse of log phase. This phase come due to accumulation of waste products and depletion of nutrients.