Bacterial growth curve

Bacterial growth curve

If a liquid medium is inoculated with bacteria and small samples are taken at a regular intervals and the number of viable cells per ml is determined periodically & plotted  or a graph in respect to time , it will give a characteristic curve known as growth curve.

Phase of growth curve:

  1.Lag phase or preparatory phase.

  2.Log phase or exponential phase.

  3.Stationary phase.

  4.Decline phase /Death phase.

1.Lag phase:

In this stage bacteria prepare for multiplication. Number of bacteria remains unchanged.

Criteria:

-No cell multiplication

-Cells adapt to new environment (media), so this is also called adaptation phase.

-Metabolic activity increases

-Cells size may increase

-Time require 1-4 hours.

2.Log phase:

Criteria:

   -Rapid cell multiplication occurs.

   -Mass increases in log manner.

   -Metabolic activity increase at a very high rate.

-   Time requires 1-4 hours.

3.Stationary phase:

Criteria:

-          At this stage, multiplication rate & death rate of bacteria equal, so neat growth rate is zero (0)

   -Exotoxin production starts at this stage.

   -P^H of the medium is changed.

   -Time requires few hours to days.

4.Death phase (Decline phase):

Criteria:

   -The death rate is greater than multiplication rate.

   -Accumulation of toxic product occurs.

   -The number of viable bacteria is decreased.

   -Time requires few hours to days.