batterjee medical college. ass. prof. dr. manal el said head of microbiology department bacteria...

Batterjee Medical College


Ass. Prof . Dr. Manal El Ass. Prof . Dr. Manal El SaidSaid

Head of Microbiology Department

Bacteria Growth and Physiology


Define the following:

a. binary fission

b. generation time

c. geometric progression

Learning Objectives for "Bacterial Growth"

After completing this section you should be able to perform

the following objectives.


• Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells.

Bacterial Reproduction (1)


Bacterial Reproduction (2)

Binary Fission


• 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.

Bacterial Growth Curve (1)


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.



1. Define the following: a. Psychrophile

b. Psychrotrophc. Mesophiled. Thermophilee. Obligate aerobef. Obligate anaerobeg. Aerotolerant anaerobeh. Facultative anaerobe

2. State the optimum pH range for most bacteria

3. Define the following: a. Phototroph

b. Chemotrophc. Autotrophd. Heterotrophe. Fastidious

Learning Objectives for "Factors Influencing Bacterial Growth"

After completing this section you should be able to perform the following objectives.


Physical Requirements

Factors Influencing Bacterial Growth

Nutritional Requirements

1. Temperature 2. Oxygen requirements 3. PH 4. Osmosis

1- Energy source 2- Carbon source 3- Nitrogen source 4- Minerals - Sulfur - Phosphorus - Potassium, magnesium & calcium - Iron - Trace elements

5- Water 6- Growth factors


1-Temperature

Factors Influencing Bacterial Growth:Physical Requirements

Definition Optimum growth temperature

Psychrophiles Cold-loving bacteria Between – 5C and 15C.

Mesophiles Bacteria that grow at moderate temperatures.

Between 20C and 40C. • Most bacteria are

mesophilic & include soil bacteria and bacteria that live in and on the body.

Thermophiles Heat-loving bacteria Between 45C and 70C.

Hyperthermophiles Bacteria that grow at very high temperatures

Between 70C and 110 C.


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

Aerotolerant anaerobes (obligate fermenters )

- Cannot use oxygen to transform energy - Can grow in its presence.

Only by fermentation

Facultative anaerobesMost bacteria

- Grow with or without oxygen- But generally better with oxygen.

-Aerobic respiration if oxygen is present

- Fermentation or anaerobic respiration if it is absent.

2- Oxygen requirements



2- Oxygen requirements (2)



3- pH

Neutrophiles Acidophiles Alkaliphiles

pH range of 5-8 ph 8.5pH 5.5

Most pathogens grow at pH 7.2 =

pH of blood and body tissues



• 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.

4- Osmosis (1)




4- Osmosis (2)

•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.

(Most bacteria)

•The water concentration is greater inside the cell & the solute concentration is higher outside .

•Water goes out of the cell.

•The water concentration is greater outside the cell &the solute concentration is higher inside.

•Water goes into the cell.



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 ).


They use the oxidation & reduction of chemical

compounds

1- Energy Source

They use sunlight to convert CO2 & water into organic materials

Factors Influencing Bacterial Growth:Nutritional Requirements (1)

Phototrophs Chemotrophs

Photosynthesis Respiration Fermentation


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- Glycolysis1- GlycolysisThe end product of glycolysis are: - 2 molecules of pyruvic acid - 2 ATP molecules.

2-The Krebs cycle2-The Krebs cycle• The substrate are the 2 molecules of pyruvic acid• Generating 2 ATP molecules.

3- Oxidative phosphorylation3- Oxidative phosphorylation (Electron transport chain) • It result in the formation of 34 ATP molecules. •The final electron acceptor is molecular O2


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.


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.


• Require organic forms of carbon.

• It cannot synthesize organic molecules from inorganic nutrients.


2- Carbon Source

HeterotrophsAutotrophs

• Require only carbon dioxide as a carbon source.

• It can synthesize organic molecules from inorganic nutrients.



3- Nitrogen Source

- Amino acids

- DNA

- RNA

- ATP

Nitrogen is needed for the synthesis of :

- Nitrogen

- Nitrates

- Ammonia

- Organic nitrogen compounds

Nitrogen sources are:


•It is needed to synthesizes sulfur-containing amino acids and certain vitamins.

•Sulfur source : - Sulfates - Hydrogen sulfide - Sulfur-containing amino acids


4- Minerals1. Sulfur

•It is needed to synthesize phospholipids, DNA, RNA & ATP.•Phosphate ions are the primary source of phosphorus.

2. Phosphorus

3. Potassium, Magnesium and Calcium

These are required for certain enzymes.



4- Minerals

•They are required in very minute amounts and function as cofactors (electron donors or acceptors) in enzyme reactions.

•They include sodium, zinc, copper, molybdenum, manganese and cobalt ions.

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



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.

They having complex nutritional requirements & needing

many growth factors

Fastidious Organisms

batterjee medical college. ass. prof. dr. manal el said head of microbiology department bacteria...

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