Growth curve of bacteria SlideShare

1. Growth Curve of
Bacteria
Food Microbiology
By Sayanta Mitra

2. What is Bacterial Growth Curve?
Bacterial growth curve is a curve on a graph that
shows the changes in number of a bacterial population
over time in a culture.
Important points :
• Not increase in size it means increase in number,
increase in population.
• Depends on favourable condition ( eg – temperature,
pH, nutrients etc)

3. • This graphical representation is for heterotrophic
bacteria; that means that type of bacteria who takes
their food or nutrients from other sources.
• The growth Curve of bacteria occurs in a geometric
or exponential manner.
(Means with each division cycle or generation one cell
gives rise to 2 cells, then 4 cells, then 8, then 16,
then 32 and so on)
• The time require for formation one single generation
is called generation time (G).

4. Phases of Bacterial Growth Curve
It has been determined that in a closed system or
batch culture (no food added, no wastes removed)
bacteria will grow in a predictable pattern, resulting in
the growth curve.
This curve consists four distinct phases:
• Lag phase
• Exponential or log phase
• Stationery phase
• Death phase

5. Lag Phase :
• Newly inoculated bacteria are adopting the new
environment. So this phase is also called
preparatory phase.
• The bacteria required the period of time between
the introduction of a microorganism into a new
culture medium and the time it begins to increase
exponentially, this period is called lag period.
• A small group of cells that are placed in a rich
nutrient medium, synthesize proteins and other
necessary molecules. These cells increase in size,
but no cell division occurs in the phase.

6. Log Phase :
• This is the time when the cells are dividing by
binary fission and doubling in numbers after each
generation time.
• The division of the bacteria is in logarithmic or
exponential way. So this phase is also called
exponential phase.
• In case of pathogenic bacteria our body try to kill
them, as they increase in number. As a result
symptoms appear at this phase.

7. Stationery Phase :
• Lack of food, nutrients and accumulation
of wate products, hence growth slow
down.
• Reproduction rate = Death rate.
• The stationary phase lasts as long until
there are no nutrients left and also there
is too much accumulation of waste.

8. Death Phase :
• Acute shortage of available food.
• Increase the secretion of toxins.
• Number of living cells decreases
exponentially.
• Death rate >> Reproduction rate.
• Ultimately the bacteria disappear
completely from that place.