1. BACTERIAL GROWTH Dr. Faten Mostafa
Professor of Medical Microbiology & Immunology,
Faculty of Medicine, Ain Shams University
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2. At the end of this chapter you should be able to:
Define bacterial growth, and generation time.
Describe the process of bacterial replication.
Demonstrate the phases of microbial growth and describe their relation to generation time.
Discuss clinical significance of growth curve.
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3. At the end of this chapter you should be able to:
Compare and contrast between autotrophic and heterotrophic bacteria regarding nutritional requirements.
Differentiate bacteria according to their gaseous requirements.
Describe physical conditions necessary for bacterial growth
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4. Short 20 minutes long. 18 hours E.coli. Mycobacteria
Growth involves both an increase in Generation Time (doubling time)
Short 20 minutes
E.coli.
long. 18 hours
Mycobacteria
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5. Doubling time (generation time)
time required for a population of bacteria cells to double
• varied from one species to another
- doubling time depends on
nutritional and genetic factors
eg. Escherichia coli doubles in ~20 min
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6. DNA DNA replication Cell separation Septum formation
Microbial growth
Binary fission:
asexual division of one cell into two
DNA
DNA replication
Septum formation
DNA is attached to membrane during separation
Cell separation
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7. Bacterial Reproduction
4-protoplasm becomes
divided into 2 equal parts by
inward growth of
CM & CW
1-Simple
binary fission
2-double stranded DNA
(bacterial chromosome)
separate
3-acts as
a template
for another copy.
5-parent cell separates into 2
daughter identical cells.
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8. 1 2 4 8 16 Exponential increase in the number of cells
Microbial growth
an increase in the number of cells 1 2 4 8 16
Exponential increase in the number of cells
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9. BACTERIAL GROWTH In Vitro
Facultative intracellular
living cells
artificial culture media
obligate
intracellular
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10. both IC
outside host can be
cultivated on artificial media
outside host
can not cultivated
Treponema pallidum (of syphilis) and Mycobacterium leprae (of leprosy) cannot grow in vitro
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11. Give reasons
chlamydia and Rickettsia can grow only within living cells
. They are obligate intracellular parasites.
is that they lack the ability to produce sufficient ATP and must use ATP produced by the host cells. •
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12. Bacterial Growth Curve
If No of bacterial cells present in any culture is measured &No is plotted in relation to time (growth period), the resulting figure is called Bacterial Growth Curve. It is formed of 4 phases
Exponential Phase (Log phase)
Stationary Phase
Decline or Death Phase
Lag Phase
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13. Bacterial Growth Curve
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14. Growth phases Lag Exponential (Log) Stationary Death log # of viable
cells
Slower growth rate
Time
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15. 6/26/2019
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16. log # of viable Lag cells Time Lag phase
cells adapt to their new environment
They start to synthesize enzymes and molecules required for bacteria growth
No cell division
length of this phase depends on the type of the organism, size of the inoculum and type of growth medium.
one hour up to several days depending
log
# of
viable
cells
Lag
Time
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17. Lag phase
an increase in bacterial mass per unit of volume, but no increase in cell count.
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18. log # of viable cells Time Exponential (log) phase
cell number increases logarithmically most active phase . cells dividing at their maximum rate of division
phase continues until the nutrient of the medium is exhausted or toxic metabolites accumulate.
Bacteria are highly susceptible to antibiotics at this phase
Exponential
(log) phase
ascending straight line. ●
log
# of
viable
cells
Time
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19. log # of viable cells Time Stationary Stationary phase
. nutrient in the medium are exhausted and toxic products accumulate, the rate of growth decrease.
The number of dying cells equal to the number of newly formed cells.
The number of viable bacteria remains constant.
Process of sporulation in spore forming bacteria start in this phase
Stationary
log
# of
viable
cells
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Time

20. log # of viable cells Time Death Death phase
exhaustion of nutrients, accumulation of waste products and harmful changes in pH continue; the rate of division becomes less and less, and the death rate increases until it reaches a steady level.
NO of dying bacteria exceeds the number of newly formed bacteria.
NOof viable living bacteria is decreasing until the population dies out entirely.
Death
log
# of
viable
cells
Time
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21. Clinical significance of bacterial Growth Curve
natural infections and diseases
Lag Phase incubation period.
Exponential &stationary Phases the clinical signs and symptoms of disease.
Decline Phase convalescence period &recovery from a disease.
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22. Growth Requirements Chemical nutritional gaseous Physical temperatureOP
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23. Nutritional requirements
Minerals
Carbon &
Nitrogen
According to carbon requirement, bacteria are subdivided
Growth
factors
utilize simple inorganic
. CO2,Ho2, and inorganic salts they synthesize organic substances proteins, carbohydrates
Sulfur,
Phosphorus,
Potassium,
Magnesium
Calcium.
Heterotrophic
Autotrophic
yeast extract,
blood,
B complex vitamins,
amino acids,
purines
pyrimidines.
Require
organic source
of carbon.
free living,
non-pathogenic
derived
from living host are called parasite
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24. Heterotrophic pathogenic or commensals according to
nitrogen requirement
nonexacting bacteria that
utilize inorganic source
of nitrogen
exacting bacteria that
utilize organic source of nitrogen.
growing only in special artificial cultures containing specific growth factors
Heterotrophic bacteria include both pathogenic and commensal
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25. N.B. Fastidious bacteria are those bacteria with complex nutritional needs.
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26. Growth Requirements O2 CO2 Gaseous (chemical ) Requirements Physical
Nutritional
requirements
Carbon &
Nitrogen
Growth
factors O2
CO2
Temperature
Inorganic
ions pH
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27. Gaseous Requirements Oxygen carbon dioxide. low O2 tension
Microaerophilic
CO­2 present in air (0.05%) is sufficient for growth
higher con of CO2 (5-10%) for growth,.
low O2 tension
Obligate aerobes
Presence of O2
Capnophilic Bactria
Obligate anaerobes
absence of O2
pathogenic Neisseria
Brucella abortus.
Facultative anaerobes
Aerobic &anaerobic
most of pathogenic bacteria
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28. Gaseous Requirements
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29. . Effect of Oxygen Some organisms require O2
Some organisms are killed by O2
Some are not affected by O2
Classes based on oxygen
requirement
1. obligate aerobes
2. microaerophiles
3. facultative anaerobes
4. strict (obligate) anaerobes
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30. require ambient concentration of O2 (21%)
1. aerobes:
require ambient concentration of
O2 (21%)
2. microaerophiles:
• grow only at low [O2]
• require O2 for aerobic respiration, but have some enzymes that are inactivated by O2
3. facultative anaerobes:
• can grow aerobically or anaerobically
• can use either O2 or another substance as the terminal
electron acceptor
4- obligate anaerobes. These bacteria grow only in absence of O2
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31. H2O2 + e- + H+  H2O + OH• hydroxyl radical OH• + e- + H+  H2O
Aerobes obtain their energy by a series of oxidation-reduction reaction in which the hydrogen acceptor is atmospheric O2 (aerobic respiration).
O e-  O superoxide
O e- + 2H+  H2O peroxide
H2O2 + e- + H+  H2O + OH• hydroxyl radical
OH• + e- + H+  H2O
Overall: O2 + 4 e H+  2 H2O
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32. Toxic forms of oxygen
Toxic, reactive oxygen species oxidize cellular macromolecules (e.g. DNA, proteins, and lipids)
O superoxide
H2O peroxide
OH• hydroxyl radical
most damaging
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33. SOD 2 H2O2  2 H2O + O2 O2- H2O2 + NADH + H+  2 H2O + NAD+
2. Adaptations to toxic oxygen:
detoxifying enzymes
ability of cells to grow in the presence of O2 depends on the presence of enzymes that eliminate these O2 toxic products, e.g. catalase enzyme which destroys H2O2 and superoxide dismutase which destroys superoxide O- radicals.
a. Catalase
2 H2O2  2 H2O + O2
b. Peroxidase
H2O2 + NADH + H+  2 H2O + NAD+
c. Superoxide dismutase (SOD)
O2- + O2-  2 H2O2 + O2
O2-
to catalase reaction
SOD
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34. SOD appears to be required for the survival of aerobes
Superoxide dismutase (SOD)
SOD appears to be required for the survival of aerobes
O2-
anaerobe •.
GR .Anaerobic bacteria lack these enzymes
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35. Facultative and anaerobic bacteria ferment, but aerobes, which can grow only in the presence of oxygen, do not.
Aerobes,, produce metabolites that enter the Krebs cycle by processes other than fermentation, such as the
deamination of amino acids
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36. but others die in the presence of oxygen (anaerobes).
Some bacteria can grow in the presence of oxygen (aerobes and facultatives),
but others die in the presence of oxygen (anaerobes).
The use of oxygen by bacteria generates toxic products such as superoxide and hydrogen peroxide.
Aerobes and facultatives have enzymes, such as superoxide dismutase and catalase, that detoxify these products, but anaerobes do not and are killed in the
presence of oxygen.
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37. Microaerophiles need oxygen because they cannot ferment or respire anaerobically. they are poisoned by high concentrations of oxygen.
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38. 6/26/2019
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39. Physical Requirements
Temperature
Hydrogen ion concentration (pH):
Psychrophilic: range (5 - 25C) (cold loving microbes ) 15 0C
most pathogenic bacteria is 6.5 and 7.5
alkaline pH
Vibrio cholerae
Mesophilic: range (25- 45C) moderate temp. loving microbes) 37 0C
acidic pH
Lactobacillus
Thermophilic: range (45 –75C) (heat loving microbes) 60 0C
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40. Non pathogenic bacteria may be psychrophilic or thermophilic
Most pathogenic bacteria are mesophilic, optimum temperature of growth at 37 0C.
Non pathogenic bacteria may be psychrophilic or thermophilic
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41. Physical Requirements
Temperature
except
except
Lower temp
Most
Higher temp
e.g ,Yerssinia pestis causing plaque grow at 27 C Why ????
1- Campylobacter and Helicobacter, both at 42 C
2- Geobacillus stearothermophilus at 120 C
Most bacteria grow at optimum temp 37 C ,Why ?/??
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42. Osmotic Pressure
 Growth of most microorganisms proceeds best when the osmotic pressure is optimum. i.e. when the salt concentration of microbial cytoplasm is the same as the external environment ( 1% NaCl; isotonic).
Microorganisms that live in marine environments can tolerate high salt concentrations.
 halophilic. 
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