Lec 03. bacterial growth

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Growth of Bacterial cell

Sebghatullah Mansoor

BS (Medical Sciences), MS (Microbiology),

MPH (Continue…)

Medical faculty of Malalay University

06/Feb/2017

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Bacteria reproduce by Binary Fission;

. A process by which one parent cell divides

to form two progeny cells. Because one cell gives rise to two progeny cells, bacteria are said to undergo exponential growth (logarithmic growth).

Bacterial Growth Cycle

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Bacterial Growth Cycle…

• 1 bacterium will produce 16 bacteria after 4 generations.

• The doubling (generation) time of bacteria ranges from as little as 20 minutes for Escherichia coli to as long as 18 hours for Mycobacterium tuberculosis.

•

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• The exponential growth and the short doubling time of some organisms result in rapid production of very large numbers of bacteria.

• For example, 1 E. coli organism will produce over 1000 progeny in about 3 hours and over 1 million in about 7 hours.

• The doubling time varies not only with the species, but also with the amount of nutrients, the temperature, the pH, and other environmental factors.

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• The growth cycle of bacteria has four major phases. If a small number of bacteria are inoculated into a liquid nutrient medium and the bacteria are counted at frequent intervals,

1. Lag Phase

2. Log (Exponential ) Phase

3. Stationary Phase

4. Decline ( Death ) Phase


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1. Lag Phase; During which energetic metabolic activity occurs but cells do not divide. This can last for a few minutes up to many hours.

• Cells not divided because?. The inadaptability of bacterium with new environment. Enzymes are formed and accumulate until they are

present in concentrations that permit growth to resume. . Genetically incapable of growth in the new medium


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Lag Phase

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2. Log (Exponential ) Phase; is when rapid cell division occurs, because of sufficient nutrients and space in the culture medium.

This phase is important for these reasons ?

. β-Lactam drugs, such as penicillin, act during this phase because the drugs are effective when cells are making peptidoglycan (i.e., when they are dividing).


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Log Phase

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3. Stationary Phase; The stationary phase occurs when nutrient reduction or toxic products cause growth to slow until the number of new cells produced balances the number of cells that die. This may take hours. The importance of this phase?

1. exhaustion of available nutrients

2. accumulation of inhibitory metabolites or end products

3. exhaustion of space, in this case called a lack of "biological space".

4. It is during the stationary phase that spore-forming bacteria have to induce or expose the activity of dozens of genes that may be involved in sporulation process.


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Log Phase

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4. Decline ( Death ) Phase ; The final phase is the death phase, which is marked by a decline in the number of viable bacteria. In this phase few of the bacteria may survive for months.


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Decline ( Death ) Phase

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All Phases

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Bacterial growth phases

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Transitional phase

• This phase is occurs while the bacteria forward from one phase to another or the time between each of the two phase.

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All the phases

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Aerobic & Anaerobic Growth

• For most organisms, an adequate supply of oxygen enhances metabolism and growth.

• The oxygen acts as the hydrogen acceptor in the final steps of energy production catalyzed by the flavoproteins and cytochromes. Because the use of oxygen generates two toxic molecules, hydrogen peroxide (H2O2) and the free radical superoxide (O2).

• Bacteria require two enzymes to utilize oxygen. The first is superoxide dismutase, which catalyzes the reaction and the second is catalase, which catalyzes the reaction

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1. Some bacteria, such as M. tuberculosis, are obligate aerobes; that is, they require oxygen to grow because their ATP-generating system is dependent on oxygen as the hydrogen acceptor.

2. Other bacteria, such as E. coli, are facultative anaerobes; they utilize oxygen, if it is present, to generate energy by respiration, but they can use the fermentation pathway to synthesize ATP in the absence of sufficient oxygen.

3. The third group of bacteria consists of the obligate anaerobes, such as Clostridium tetani, which cannot grow in the presence of oxygen because they lack either superoxide dismutase or catalase, or both. Obligate anaerobes vary in their response to oxygen exposure; some can survive but are not able to grow, whereas others are killed rapidly.

Aerobic & Anaerobic Growth

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Some important other types of Bacteria

• Mycoplasma

• Spirochetes

• Actinomycetes

• Rickettsia

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Mycoplasma• There are more than 200 known species in the class of Mollicutes (cell wall–free bacteria).

• Mycoplasmas are the smallest organisms that can be free living in nature and self-replicating on laboratory media

• They have the following characteristics

– The smallest mycoplasmas are 125–250 nm in size

– They are highly pleomorphic because they lack a rigid cell wall, they contains a sterol, can be seen as (round, rod, filament and granules)

– Mycoplasmas are completely resistant to penicillin because they lack the cell wall structures at which penicillin acts.

– Border line between virus and bacteria

– Can not be seen by light microscope, electron microscope required

– We can stain with Giemsa stain

– Replicate by binary fission,

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• At least 16 of these species are thought to be of human origin; others have been isolated from animals and plants.

• In humans, four species are of primary importance:

1. Mycoplasma pneumoniae.

2. Mycoplasma hominis

3. Ureaplasma urealyticum

4. Mycoplasma genitalium

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Mycoplasma…

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Mycoplasma…

Spirochetes • Spirochetes are thin-walled, flexible, spiral rods • They are motile through the undulation of axial filaments that lie under the outer

sheath. Treponemes and leptospirae are so thin that they are seen only by dark field microscopy, or immunofluorescence.

• Borreliae are larger, accept Giemsa and other blood stains, and can be seen in the standard light microscope.

• Family ( Spirochaetaceae ) consists of two genera whose members are human pathogens

• Borrelia and Treponema . • The other family (Leptospiraceae) includes three genera:• Leptospira , Leptonema , and Turneriella . • They are long, slender, helically coiled, spiral or corkscrew- shaped bacilli.• T. pallidum has an outer sheath or glycosaminoglycan coating.

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Spirochetes… ( Electron microscopy)

Actinomycetes

• Actinomycetes are a family of bacteria that form long, branching filaments that resemble the hyphae of fungi .

• They are related to the corynebacteria and include multiple genera of clinical significance such as Mycobacteria and saprophytic organisms such as Streptomyces

• They are gram-positive, but some (such as Nocardia asteroides) are also weakly acid-fast rods

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Rickettsia

• Rickettsiae are obligate intracellular bacteria; that is, they can grow only within cells.

• They are the agents of typhus, spotted fevers, and Q fever.

• Rickettsiae are very short rods that are barely visible in the light microscope. Structurally, their cell wall resembles that of gram-negative rods, but they stain poorly with the standard Gram stain.

Example ;

— Rickettsia typhi

— Rickettsia prowazeki

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THANK YOUQuestions ?

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Health & Medicine

Lec 03. bacterial growth