Bacterial growth curve

1. BACTERIAL
GROWTH CURVE
Chaitali Kalamkar.S
Asst.Prof
Arihant COP, Ahmednagar

2. Introduction
■ Growth is defined as increase In cellular constituten which
lead to rise in cell number.
■ Microorganism is reproduced by binary fission and
budding.The cells copy their DNA almost continuously and
divide again and again by the process called Binary fission
■ Binary fission is a form of asexual reproduction in single
celled organisms by which one cell divides into two cells of the
same size.

3. Fig.Binary fission reproduction

4. Bacterial growth curve.
■ Bacteria’s growth can take place by binary fission and during
that so many phases happen during that different events take
place.
■ Five type of growth curves....
1. Growth cycle (Growth curves)
2. Biphasic growth
3. Maintenance of cells in exponential phase
4. Synchronous growth
5. Bacterial growth in vivo

5. Bacterial Growth curve..
■ The increase in cell number or growth in population is studied
by analyzing the growth curve of microbial culture.
■ Bacteria can be grown or cultivated in a liquid medium in a
closed system or also called as batch culture
■ In this method ,no fresh Medium is added and hence with time,
nutrient concentration decrease and an increase in wastes is
seen.
■ As Bacteria reproduce by binary fission ,the growth can be
plotted as the logarithm of the number of viable cells verses the
of incubation.

6. Bacterial growth curve...
■ The growth curve has got four phase:
1. Lag phase
2. Log phase
3. Stationery phase
4. Decline phase

7. Bacterial growth curve...

8. 1. Lag 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 become acclimatized 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
appreciable 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.
■ The average time of lag phase is 2 hours but it varies from species to
species and ranges between 1-4 hours.

9. 2. Log phase:
■ In this phase, the bacteria undergo cell division and their
population increase exponentially at a logarithmic rate. Hence
this phase is also known as exponential phase.
■ 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.
■ . The number of viable count, when plotted against time it gives
a straight line of inclined fashion.
■ The average time of log phase is 8 hours but also varies with the
bacterial species.

10. 3. Stationary phase:
■ 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.
■ Bacteria become Gram variable and show irregular staining.
■ Many bacteria start producing exotoxins.
■ Total cell number increases at a slow rate, but the viable count remains almost constant.
■ The duration of this phase is varies from few days to few hours.

11. 4. Decline phase:
■ 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.
■ The cells attain maximum size at the end of lag phase and
become smaller in log phase.

12. Summary
■ Lag Phase — i.e., at initial stages there exist almost little growth of
bacteria,
■ Exponential (or Log) Phase — i.e., showing a rather rapid growth,
■ Stationary Phase — i.e., depicting clearly a levelling off growth of
microbes, and
■ Death (or Decline) Phase — i.e., showing a clear cut decline in the viable
population of microorganismss.

13. Thank you
– “If you are working on
something that you
really care about, you
don’t have to be
pushed. The vision pulls
you.” – Steve Jobs