Transcript 0-bacterial-physiology&growth

Batterjee Medical College
Batterjee Medical College
Bacteria Growth
and Physiology
Ass. Prof . Dr. Manal El Said
Head of Microbiology Department
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Batterjee Medical College
Learning Objectives for
"Bacterial Growth"
After completing this section you should be able to perform
the following objectives.
Define the following:
a. binary fission
b. generation time
c. geometric progression
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Bacterial Reproduction (1)
• Bacteria reproduce by binary fission, a process by which
one parent cell divides to form two progeny cells.
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Bacterial Reproduction (2)
Binary Fission
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Bacterial Growth Curve (1)
• Exponential growth (logarithmic growth):
one cell gives rise to two progeny cells
• The doubling (generation) time of bacteria:
• It is the time it takes for a population of bacteria to double in
number.
• It ranges from 20 minutes for Escherichia coli to more than
24 hours for Mycobacterium tuberculosis.
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Bacterial Growth Curve (2)
The growth cycle of bacteria has four major phases
The standard growth curve can be demonstrated:
If a small number of bacteria are inoculated into a liquid nutrient medium
and the bacteria are counted at frequent intervals
1- The lag phase:
During which metabolic activity occurs but cells do not divide (few
minutes up to many hours).
2- The log (logarithmic or Exponential ) phase:
- Rapid cell division occurs.
-β -Lactam drugs (e.g. penicillin) act during this phase because they are
effective when cells are dividing.
3- The stationary phase:
Nutrient depletion or toxic products cause growth to slow until no. of
new cells balances no. of cells death resulting in a steady state.
4-The death phase:
- Decline in the number of viable bacteria.
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Bacterial Growth Curve (3)
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Learning Objectives for
"Factors Influencing Bacterial Growth"
After completing this section you should be able to perform the following
objectives.
1. Define the following:
a. Psychrophile
b. Psychrotroph
c. Mesophile
d. Thermophile
e. Obligate aerobe
f. Obligate anaerobe
g. Aerotolerant anaerobe
h. Facultative anaerobe
2. State the optimum pH range for most bacteria
3. Define the following:
a. Phototroph
b. Chemotroph
c. Autotroph
d. Heterotroph
e. Fastidious
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Factors Influencing Bacterial Growth
Physical Requirements
1. Temperature
2. Oxygen requirements
3. PH
4. Osmosis
Nutritional Requirements
1- Energy source
2- Carbon source
3- Nitrogen source
4- Minerals
- Sulfur
- Phosphorus
- Potassium, magnesium & calcium
- Iron
- Trace elements
5- Water
6- Growth factors
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Factors Influencing Bacterial Growth:
Physical Requirements
1-Temperature
Definition
Optimum growth temperature
Psychrophiles
Cold-loving bacteria Between – 5C and 15C.
Mesophiles
Bacteria that grow
at moderate
temperatures.
Thermophiles
Heat-loving bacteria Between 45C and 70C.
Hyperthermophiles Bacteria that grow
at very high
temperatures
Between 20C and 40C.
• Most
bacteria
are
mesophilic & include soil
bacteria and bacteria that
live in and on the body.
Between 70C and 110 C.
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Factors Influencing Bacterial Growth:
Physical Requirements
2- Oxygen requirements
Definition
They obtain energy through
Obligate aerobes
Grow only in the presence of oxygen
Aerobic respiration
Microaerophiles
- Require a low concentration of
oxygen (2% to 10%) for growth
- Higher concentrations are
inhibitory
Aerobic respiration
Obligate anaerobes
Grow only in the absence of oxygen
(inhibited or killed by its presence).
- Anaerobic respiration
-or fermentation
- Cannot use oxygen to transform
Aerotolerant
anaerobes (obligate energy
- Can grow in its presence.
fermenters )
Facultative
anaerobes
Most bacteria
- Grow with or without oxygen
- But generally better with oxygen.
Only by fermentation
-Aerobic
respiration
if
oxygen is present
- Fermentation or anaerobic
respiration if it is absent.
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Factors Influencing Bacterial Growth:
Physical Requirements
2- Oxygen requirements (2)
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Factors Influencing Bacterial Growth:
Physical Requirements
3- pH
Neutrophiles
pH range of 5-8
Acidophiles
pH
Alkaliphiles
5.5
Most pathogens grow at pH 7.2
=
pH of blood and body tissues
ph 8.5
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Factors Influencing Bacterial Growth:
Physical Requirements
4- Osmosis (1)
• Osmosis is the diffusion of water
across a membrane:
-From higher water concentration
(lower solute concentration)
-To lower water concentration
(higher solute concentration)
• Osmosis does not require energy.
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Factors Influencing Bacterial Growth:
Physical Requirements
4- Osmosis (2)
(Most bacteria)
•The water concentration
is greater outside the cell
&the solute concentration
is higher inside.
•Water goes into the cell.
•Both the water and
solute concentration are
the same inside and
outside the cell
•Water goes into & out of
the cell at an equal rate.
•The water concentration
is greater inside the cell &
the solute concentration
is higher outside .
•Water goes out of the cell.
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Factors Influencing Bacterial Growth:
Physical Requirements
4- Osmosis (3)
Osmotolerant Organisms :can grow at high salt concentration (up to 10%).
Halophiles : require high salt concentrations for growth, (up to 20% or higher ).
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Factors Influencing Bacterial Growth:
Nutritional Requirements (1)
1- Energy Source
Chemotrophs
Phototrophs
They use sunlight to
convert CO2 & water into
organic materials
Photosynthesis
They use the oxidation &
reduction of chemical
compounds
Respiration
Fermentation
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Respiration:
1- Aerobic Respiration
•It is glucose catabolism under aerobic condition.
•This results in the production of energy in the form of 38 ATP
molecules. Aerobic respiration involves :
1- Glycolysis
The end product of glycolysis are:
- 2 molecules of pyruvic acid
- 2 ATP molecules.
2-The Krebs cycle
• The substrate are the 2 molecules of pyruvic acid
• Generating 2 ATP molecules.
3- Oxidative phosphorylation (Electron transport chain)
• It result in the formation of 34 ATP molecules.
•The final electron acceptor is molecular O2
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Respiration:
2- Anaerobic Respiration
•It occurs in the absence of oxygen.
•The final electron acceptor is an organic molecule such as
nitrate, sulfate or CO2
•There is also:
- Glycolysis,
- Krebs cycle
- Oxidative phosphorylation
•Because nitrate, sulfate or CO2 are not good electron
acceptor as oxygen, the net yield of ATP molecules is less
than it is with aerobic respiration.
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3- Fermentation
• It is the process of extracting energy from the oxidation of
organic compounds, such as carbohydrates, and using an
endogenous electron acceptor, which is usually an organic
compound.
• The sugar breakdown to pyruvic acid and then, to lactic acid
or ethanol.
• It is the process by which facultative bacteria generate ATP
in the absence of oxygen.
• There is no oxidative phosphorylation.
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Factors Influencing Bacterial Growth:
Nutritional Requirements (2)
2- Carbon Source
Autotrophs
• Require only carbon
dioxide as a carbon
source.
• It
can
synthesize
organic molecules from
inorganic nutrients.
Heterotrophs
• Require organic forms
of carbon.
• It cannot synthesize
organic molecules from
inorganic nutrients.
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Factors Influencing Bacterial Growth:
Nutritional Requirements (3)
3- Nitrogen Source
Nitrogen sources are:
- Nitrogen
- Nitrates
- Ammonia
- Organic nitrogen compounds
Nitrogen is needed for the synthesis of :
- Amino acids
- DNA
- RNA
- ATP
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Factors Influencing Bacterial Growth:
Nutritional Requirements (4)
4- Minerals
1. Sulfur
•It is needed to synthesizes sulfur-containing amino acids
and certain vitamins.
•Sulfur source :
- Sulfates
- Hydrogen sulfide
- Sulfur-containing amino acids
2. Phosphorus
•It is needed to synthesize phospholipids, DNA, RNA & ATP.
•Phosphate ions are the primary source of phosphorus.
3. Potassium, Magnesium and Calcium
These are required for certain enzymes.
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Factors Influencing Bacterial Growth:
Nutritional Requirements (5)
4- Minerals
4. Iron
-It is component of cytochromes and other enzymes.
-Bacteria produce iron-binding compounds (siderophores)
which capture iron by chelating it, attach to specific
receptors & actively transported into the cell.
5. Trace Elements
•They are required in very minute amounts and function as
cofactors (electron donors or acceptors) in enzyme reactions.
•They include sodium, zinc,
manganese and cobalt ions.
copper,
molybdenum,
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Factors Influencing Bacterial Growth:
Nutritional Requirements (5)
5- Water & 6- Growth factors
• Growth factors are organic compounds such as:
- Amino acids
- Purines
- Pyrimidines
- Vitamins
• Cell must have them for growth but cannot synthesize itself.
Fastidious Organisms
They having complex nutritional requirements & needing
many growth factors