1. Microbial
Growth
When microbes are provided with nutrients & required
environmental factors, they become metabolically active and
grow
1Lecturer:: Mohamed Ali. Bsc, M.Eng
College of Agriculture, University Of Hargeisa.
3. What is Microbial growth?
involves an increase in the number of
cells rather than in the size of individual
cells.
2 levels of growth:
1. A cell synthesizes new components,
increase its size
2. Increase number of cells in the
population
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4. increase in cellular constituents that
may result in:
increase in cell number
e.g., when microorganisms reproduce by
budding or binary fission
increase in cell size
e.g., some microorganisms have nuclear
divisions that are not accompanied by cell
divisions
microbiologists usually study population
growth rather than growth of individual
cells
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5. 1- The Bacterial division/reproduction
Bacteria normally reproduce by a method
called binary fission
What is Binary Fission.?
Binary Fission is the process of bacteria
reproduction where one cell become two
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7. Generation Time (Doubling time)
What is Generation
Time?
The time required
for a cell to divide
(and its population
to double) is called
the generation time
As you seen in the
picture, cell’s
division produces
two cells, two cells’
divisions produce
four cells, and so
on. 7
11. 2-Stages in Bacterial Growth curve
When a few bacteria are inoculated into a liquid growth
medium, it is possible to plot a bacterial growth curve
that shows the growth of cells over time (See picture).
There are four basic phases of growth: 1- the lag, 2- log
(Exponential) , 3- stationary, and 4-death phases.
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12. Stages of Bacterial growth curve
Bacterial populations follow a sequential
series of growth phases: the lag, log,
stationary, and death phases.
Knowledge of the bacterial growth curve is
critical to understanding population
dynamics and population control in the
course of infectious diseases, and in food
preservation .
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13. no increase
maximal rate of division
and population growth
population growth ceases
decline in
population
size
4 Stages of Bacterial growth Curve
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14. a) Lag Phase
Bacteria are first introduced into an environment
or media culture.
Bacteria are trying to adapt to nutrients
Lag phase-preparing to grow in size and synthesize
enzymes etc.
varies in length
in some cases can be very short or even absent
Stages of Bacteria growth Curve
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15. b) Log (Exponential) Phase
also called log phase
rate of growth is constant
Population number of cells undergoing
binary fission doubles at a constant
interval called generation time
Continue as long as cells have adequate
nutrients & good environment
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16. c) Stationary Phase
If exponential growth continued
unchecked, startlingly large numbers of
cells could arise.
In this stage microbial death is equal to microbial
growth e-g Death=growth.
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17. Possible reasons for entry into
stationary phase
nutrient limitation
limited oxygen availability
toxic waste accumulation
critical population density reached
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18. d) Death Phase
Decline in the number of viable cells
cells dying, usually at exponential rate
Death; loss of ability to reproduce
in some cases, death rate slows due to
accumulation of resistant cells
Slower than log phase
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19. 3- Measurement of
Microbial Growth
can measure changes in number of cells
in a population
can measure changes in mass of
population
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20. Measurement of Cell Numbers
What are the lab equipment's used to
measure bacteria cell numbers?
There are two types :-
1- Direct cell counts:-
a) counting chambers
b) electronic counters
c) on membrane filters
2- Viable cell counts
plating methods (spread, pour plate)
membrane filtration methods 20
21. a) Counting chambers
easy, inexpensive, and quick
useful for counting both eucaryotes and
procaryotes
cannot distinguish living from dead cells
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22. b) Electronic counters
Such as Coulter counter
microbial suspension forced
through small hole or orifice
movement of microbe through
orifice impacts electric current
that flows through orifice
cannot distinguish living from
dead cells
quick and easy to use
useful for large
microorganisms and blood
cells, but not prokaryotes
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23. c) membrane filters
cells filtered through special membrane that
provides dark background for observing cells
cells are stained with fluorescent dyes
useful for counting bacteria
with certain dyes, can distinguish living from dead
cells
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24. 4- Important environmental factors
affect microbial growth
1.pH
2.Temperature
3.Gas requirement
4.Pressure
5.And other environmental factors e-g
radiation, water activities etc.
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25. 1. pH
negative
logarithm of the
hydrogen ion
concentration
Affect the activity
& integrity of
enzymes &
structural
components of a
cell
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26. pH
Optimum pH for most microbes ranges
approximately from 6 to 8
acidophiles
growth optimum between pH 0 and pH 5.5
neutrophiles
growth optimum between pH 5.5 and pH 7
alkalophiles
growth optimum between pH8.5 and pH 11.5
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29. Pychrophiles
grow well at Oo
C
optimum growth at 15o
C or lower
(cold loving microbes )
Cannot grow above 20o
C
Psychrotroph
can grow at 0-7o
C
optimum between 20-30o
C,
max around 35o
C
Mesophiles
growth optimum around 20-40o
C
(moderate temp. loving microbes)
Thermophiles
Growth range is 45o
C and 80o
C
optimum between 55-65o
C
(heat loving microbes)
Hyperthermophiles
optimum growth between 80o
C and 100o
C
May grow to temperatures of 120o
C
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31. Depends the kinds of microorganism, some
microorganism need oxygen while others not
need oxygen to grow
3. Gas Requirements
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Thioglycollate broth:
1. Aerobic (pseudomonas aeruginosa)
2. Facultative (Staphylococcus aureus)
3. Facultative (Escherichia coli)
4. Obligate Anaerobe (Clostridium
butyricum)
33. 4. Pressure
Microbes obtain almost all their nutrients
in solution from surrounding water
barophile organisms
Adapted to life under high pressure
require or grow more rapidly in the
presence of increased pressure
Example : bottom dwellers in the ocean
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34. Review Questions
1) What are the four stages of microbial growth? Explain
what happens each phase?
2) Name 3 direct methods use to measure microbial cell
numbers?
3) Name 2 methods used measure viable cell counts
4) What are the four environmental factors effect microbial
growth?
5) What is binary fission?
6) What is generation (doubling time)?
7) State 4 possible reasons why bacterial growth curve
entry into stationary phase?
8) How does pH effect microbial growth?
9) What is microbial growth? 34