BACTERIA - PowerPoint Presentation

Slide1

BACTERIA

CLS 311: Basic BacteriologyMrs. Amany Ahmed NiazySlide2

Bacterial StructureSlide3

Bacterial Structure

Bacterial

Structure

Exterior

Structures (cell envelope)

Capsule

Cell Wall

Cell Membrane

Filamentous ProteinAppendages

Flagella

Pili

Interior Structures

Cytosol (cytoplasm of the prokaryotic

cells

)

Ribosomes

Nucleoid

Plasmids

Endo

s

poresSlide4

Exterior Structures

The exterior structure (cell envelope) is made up of two to three layers:In

some species of bacteria an outer capsule.

C

ell

wall.

C

ytoplasmic membrane.Slide5

Capsule

The capsule is a major virulence factor in the major disease-causing bacteria, such asStreptococcus pneumoniae

.

(

Noncapsulated

mutants of these organisms are

avirulent

, i.e. they don't cause disease).

Some bacteria surround themselves with Capsule.

Most capsules are polysaccharides made of single or multiple types of sugar.

Capsule do not contribute to growth and multiplication.

Capsules provide some general protection for bacteria

eg

. Protect it from drying. .

Capsule major function in pathogenic bacteria is protection from the immune system (protect it from

phagocytosis

). Slide6

Bacterial capsules are non-ionic, so neither acidic nor basic stains will adhere to their surfaces

. The medium in which the culture is grown as well as the temperature at which it is grown and the age of the culture will affect capsule formationSlide7

Cell Wall – Why is it important?

The rigid cell wall gives the bacterium its shape and surrounds the cytoplasmic membrane, protecting it from the environment.

The strength of the wall is responsible for keeping the cell from bursting when there are large differences in osmotic pressure between the cytoplasm and the environment

.

It also helps to anchor appendages like the

pili

and flagella, which originate in the cytoplasmic membrane and protrude through the wall to the outside. Slide8

Structure of Cell Wall

Peptidoglycan is a huge polymer of interlocking chains of identical monomers. The backbone of the peptidoglycan molecule is composed of two derivatives of glucose: N-acetylglucosamine (NAG) and N-acetlymuramic

acid (NAM). The NAG and NAM strands are connected by

interpeptide

bridges.

The cell wall of bacteria is composed of peptidoglycan, which covers the entire surface of the cell. It is made up of a combination of peptide bonds and carbohydrates (protein

-sugar

)Slide9

Cell Wall

Several antibiotics (penicillins) stop bacterial infections by interfering with cell wall synthesis, while having no effects on human cells. Slide10

Classify pathogenic bacteria is on the basis of

Gram Staining and Shape.Gram Stain

Gram Positive

Gram Negative

Cocci

Rods

Rods

CocciSlide11
Slide12

Structure of Cell Wall

The wall of a bacterium is classified in two ways:Gram-positive. A gram-positive cell wall has many layers of peptidoglygan

(up to 90% of the cell wall). Which makes it

retain the crystal

violet

dye when the cell is stained. This gives the cell a purple color when seen under a microscope

.

The cell wall also contain

Teichoic & lipoteichoic acids which

promote adhesion and anchor wall to membrane.

Gram-negative

.

The cell walls of

gram negative

bacteria are more chemically

complex.

Peptidoglycan makes up only 5 – 20% of the cell wall, and is not the outermost layer, but lies between the plasma membrane and an outer membrane

.

This outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS)

.

LPS

is a harmful substance classified as an

endotoxin

.Slide13

The Outer Membrane Of Gram Negative Bacteria.

Unique lipid by layer imbedded by protein. It contain Porins 

specialized channel-forming proteins that can allow small molecules and ions to cross the outer membrane.

It is made up of lipid

bilayer

where the outside layer is made up of

lipopolysaccharides

(LPS)Eg

. Lipid A



it is protein of LPS small amount of Lipid A stimulate immunity and defense system responds effectively and eliminate the invader.

Lipid A large amounts example in GNR in blood stream the defense system

damage even our won cells and this is the symptoms associated with

endotoxin

.

O-specific polysaccharide



it

differes

among species of bacteria and it can be used to identify species or strains.

Eg

.

E.coli

O157:H7Slide14

Structure of Cell Wall Slide15

Peptidoglycan and Antibiotics

Some antibiotics such as Penicillins and Cephalosporins, interfere with the linking of the interpeptides

of peptidoglycan, but because of the LPS membrane, these antimicrobials can’t access the peptidoglycan of

gram-negative bacteria

.

While

gram

-positive bacteria

, are more susceptible to these antibiotics because of the lack of the LPS (lipopolysaccharides).

Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs. Slide16

There are two main types of bacterial cell walls,

Gram positive and Gram negative, which are differentiated by their Gram staining characteristics. Gram stain Procedure:

Crystal violet

Iodine

Alcohol

Saffranine

GRAM STAINSlide17

Gram stainSlide18

Gram +

veandGram –veCell Wall

Gram Positive

Color of Bacteria:

Blue-violet

Gram Negative

Color of Bacteria:

REDSlide19

Cell Membrane (=cytoplasmic membrane)Slide20

Cell Membrane (=cytoplasmic membrane)

Cell membrane is composed of phospholipids bilayer and proteins which is found through out the living world.

It is responsible for selective and active transport of materials in and out of the cell.

It is involved in secretion of some exotoxins and hydrolytic enzymes involved in the pathogenesis of disease. Slide21

Cell Membrane (=cytoplasmic membrane)

It contain many proteinsThose proteins are constantly moving. For example: more than 200 different membrane proteins have been found in E.coli. Many act as a receptores. Slide22

Cell Membrane Permeability

Simple Diffusion: Water small hydrophobic molecules and gases.Transport system: Facilitated diffusion 

passive transport.

Moving in and out until their concentration is same on

bothy

side of the membrane.

It only eliminate difference in concentration but cannot create one.

Active transport



move compounds against concentration gradient. Slide23

Filamentous Protein AppendagesAnchored in the

cytoplasmic membrane and protrude out from the surface. Not essential but help in survival. Slide24

Flagella, Appendages

Flagella (singular, flagellum) are long hair like protein structure that are found in many species of bacteria. They may

be found at either or both ends of a bacterium or all over its surface.

Function of the Flagella:

the flagella beat in a propeller-like motion to help the bacterium move toward

nutrients, or away

from toxic

chemicals.Slide25

Flagella, Appendages

It can rotate > 100,000 revolutions /min (move bacteria 20 body lengths/sec)Eg. Helicobacter pylori multiple flagella at one end  allow it to penetrate the viscous mucous gel that coats the stomach epithelium . Slide26
Slide27

Structure of FlagellaSlide28

Structure of Flagella

Filament  the portion extending into the exterior environment. It is composed of identical subunits of a protein called flagellin. Which form a helical structure with a hollow core.

Basal Body



anchors the flagellum to the cell membrane.

Gram negative contain 2 pairs of rings.

Gram positive  contain 1 pair of ring.

Hook 

connect the filament to the cell surface. Slide29

A) Tumbles

last only a fraction of a second, which is sufficient to effectively randomize the direction of the next run.

B) Runs

tend to be variable in length extending from a fraction of a second to several minutes

Cells tumble less frequently when they sense they are moving closer to an attractant.

In contrast they tumble more frequently when they sense they are moving closer to a repellent.

Slide30

Flagella, Appendages

Example of movements: Chemotaxis 

bacteria moves toward a compound if it is a nutrient.

Phototaxis



some bacteria respond to variations in light.

Aerotaxis



bacteria respond to concentration

fo

oxygen. Slide31

Pili, Appendages

Pili(singular, pilus) are short hair-like projections found all around the surface of cells of many bacteria.

Composed of protein subunits arranged helically to form a long cylindrical molecule with a hollow core.Slide32

Function of the Pili

To enable attachment of cells to specific surfaces . It adhere by binding to a very specific molecule (called fimbriae). (e.g.

E.coli

that cause severe watery diarrhea attach to the cells that line the small intestine through specific interactions between

pili

and intestine surface).

Without

pili

, many disease-causing bacteria lose their ability to infect because they are unable to attach to host tissue.

It play a role in movement of population of cells on solid media.

Some are called sex

pilus

because it is used to join one bacterium to another as a bridge for specific type of DNA transfer. Slide33

Sex

PiliSlide34

Pili

, Appendages Slide35

C

ytosol (cytoplasm of the bacteria)It is where the functions for cell growth, metabolism, and replication are carried out. It

is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and

contains cell structures such as ribosomes, a

Nucleoid,

and plasmids

.

The cell envelope encases the cytoplasm and all its components.

Unlike the eukaryotic (true) cells, bacteria do not have a membrane enclosed nucleus.The chromosome, a single, continuous strand of DNA, is localized, but not contained, in a region of the cell called the

nucleoid

. All the other cellular components are scattered throughout the cytoplasm.Slide36

The Nucleoid

The chromosome of prokaryotes is an irregular mass within the cytoplasm, that is usually attached to the cytoplasmic membrane.It is usually a large, circular molecule of double-stranded DNA. It is usually tightly packed into about 10% of the total volume of the cell. The absence of nuclear membrane is very important for rapid growth or prokaryotic cells in changing environments.

The

nucleoid

is a region of cytoplasm where the chromosomal DNA (chromosome) is located.

NucleoidSlide37

Ribosomes

Involved in protein synthesis, they translate the genetic code form nucleic acid to that of amino acids

It is much more abundant than in the cytoplasm of eukaryotic cells

 this is a reflection of the higher growth rate of bacteria.

Ribosomes of prokaryotic cells 70S

(composed of 2 subunits 30S – 50S)

are smaller in size than ribosomes of eukaryotic cells 80S.

They differ in structure

wich

make them a target for certain antibiotics.

RibosomesSlide38

Storage Granules

Used to store nutrient that the cell has in relative excess. Bacteria use granules to store minerals and nutrients (lipids, carbohydrates, phosphates, sulfur or metals) for the cell to use when needed.Slide39

Plasmids

Plasmids are small usually circular, double-stranded DNA.It is separated from the chromosome, and they are not involved in reproduction. They are found in many strains of bacteria. A single bacterial cell can harbor multiple types of plasmids.

Plasmids replicate independently of the chromosome

and, while not essential for survival, appear to give bacteria a selective advantage. For example, many plasmids code for the production of one or more enzymes that destroy certain antibiotics (resistance to that antibiotic). Slide40

How are plasmids passed on from one bacteria to the other??

Plasmids are passed-on to other bacteria through Two ways: 1. For most plasmid types, copies in the cytoplasm are passed on to daughter cells during binary fission

. Slide41

How are plasmids passed on from one bacteria to the other??

Other types of plasmids form a tube-like structure at the surface called a pilus that passes copies of the plasmid to other bacteria during conjugation, a process by which bacteria exchange genetic information.Slide42

Plasmids

Many plasmid genes promote survival and pathogenesis. Plasmid are responsible for transfer of cellular properties such as, production of toxins, production of pili , resistance to antimicrobials and other toxic chemicals. The ability to insert specific genes into plasmids have made them extremely useful tools in the fields of molecular biology and genetics, specifically in the area of

genetic engineering.Slide43

Bacterial Structure

Bacterial

Structure

Exterior

Structures

Capsule

Cell Wall

Cell Membrane

Filamentous ProteinAppendages

Flagella

Pili

Interior Structures

Cytosol (cytoplasm of the prokaryotic

cells

)

Ribosomes

Nucleoid

Plasmids

EndosporesSlide44

Endospores

Resistance of spore is due to dehydrated state, and specialized coats. Germination of spores reproduces cell identical to that which was

sporulated

.

Endospores are bacterial

survival structures

that are

highly resistant

to many different types of chemical and environmental stresses and therefore enable the survival of bacteria in environments that would be lethal for these cells in their normal vegetative form.Slide45

Endospores

Endospores may remain dormant for 100 years or even longer. Immersion in boiling water for hours may not kill them. Endospores that survive these treatments can germinate or exit the dormant stage, to become a typical multiplying cell, called a vegetative cell. They can be found virtually anywhere. (cultivating media, soil, medical devices, food…etc)

Example of

endo

-spore forming bacteria

Clostridium

botulinum

Clostridium

tetani

Clostridium

perfringens

Bacillus

anthracis

. Slide46
Slide47

Spore Coat

 proteinCore Wall and Cortex  peptidoglycanCore  metabolically inactive cell with low water content.

When the environmental conditions are suitable, the

endospore

absorbs water, swells and the wall splits, releasing the cell inside. It develops a new cell wall and starts functioning as a typical bacterial cell.

Slide48
Slide49

Location of endosporeSlide50

Cell Morphology & Shape of Bacteria

Coccus

(

spherical):e.g.

Streptococci

, Staphylococci

Bacillus

(rod-like)

:

e.g.

Enterobacteriacea

spp.

Spirillum

(spiral):

e.g.

Treponema

spp.Slide51

Bacteria typically have one of three shapes

:

spheres (

cocci

).

rods

(bacilli)

,

spiral (spirilla

).

Unicellular

, they often stick together forming clumps or filaments.Slide52
Slide53

Replication of Bacteria

Bacterial cells replicate asexuallyby a process called:

Binary Fission

.

One cell doubles in size and splits in half to produce two identical daughter cells. These daughter cells can then double in size again to produce four sibling cells and these to produce eight, and so on.

Doubling Time:

the time it takes for a bacterial cell to grow and divide in two.

When nutrients are plentiful, the doubling time of some bacterial species can be as short as 20 minutes. However, most bacterial species show a doubling time between 1-4 hours. Slide54
Slide55
Slide56

DNA

Duplicate of original molecule

RNA

Transcription

Translation

Protein

Replication

Replication of Chromosomal DNA of ProkaryotesSlide57

Replication of Bacteria

The cytoplasm of a bacterial cell contains the DNA moleculesthat make up the bacterial genome.Transcriptional machinery

copies DNA into ribonucleic acid (RNA).

R

ibosomes

translate the messenger RNA information into proteinsequence. Slide58

Replication of Bacteria

Since there is no nucleus, all of these processes occur simultaneously. The rapid growth rateof the bacterial cell requires constant DNA replication and ways to segregate the two new chromosomesinto the two daughter cells without tangling them.Slide59

When germ relationship go bad..