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1/10th the size of eukaryotic cells
Flagella-long hair-like structure used for
Reproduce asexually –Binary Fission
Size of bacteria:
Bacteria are so small because of that their size is
measured in a micron (u )
Generally cocci are about 1u in diameter and
bacilli are 2 to 10 u in length and 0.2 to 0.5 u in
The limit of resolution with unaided eye is about
200 u because of that bacteria can be only
visualized under microscope.
Shape of bacteria:
Cocci in cluster – staphylococci
Cocci in chain – streptococci
Cocci in pair- diplococci
Cocci in group of four – tetrad
Cocci in group of eight – sarcina
• In the bacteria the outer layer or cell envelop or
bacteria consist of two things
(a) rigid cell wall
(b) underlying cytoplasmic membrane or
it includes granules, ribosomes,
mesosomes and circular DNA.
Some bacteria in addition to possess aditional
structures such as gelatinous material which
cover it is called as capsule and when it is too
thin it is called as microcapsule.
most cell posses a cell envelop
consisting of cell wall and underlying
“the tough, rigid structure which
surrounds bacterial cell it is called as cell wall”
• Thickness: 10-20nm
• Weight: 20-25% of dry weight of bacterial cell
Chemical structure of cell wall:
Chemical structure of cell wall is made up of a Peptido-
glycan Polymer (amino acids + sugars)
That structure is unique to all bacteria
Sugars; NAG & NAM
Amino acids cross link NAG & NAM
Made of peptidoglycan – a combination of protein and
It is present in both gram positive & negative bacteria.
Some bacteria called Gram negative bacteria have an additional
layer of membrane that contains lipopolysaccharide
- this extra layer inhibits the uptake of antibiotics – protecting the
Gram negative cell wall:
Lipoprotein layer: it connects the peptidoglycan
to outer membrane
Outer membrane : this contain certain proteins
that work as a target sites for antibiotics.
Lipopolysaccharide : it consist endotoxins
( which are responsible for pyrogenecity, lethal
effect, tissue necrosis)
Periplasmic space : it is the space between
inner & outer membrane which contains
important proteins and oligosaccharides.
Gram positive cell wall:
Peptidoglycan layer : in gram positive bacteria
peptidoglycan layer is thicker( 15-25 nm ) than
gram negative bacteria ( 10-15 nm )
Gram positive cell wall contains antigens such
as polysaccharide & proteins.
1) protection of internal structure
2)Gives shape to the cell
3) confers rigidity & ductility
4) role in division of bacteria
5) offers resistance to harmful effect of
6) contains receptor sites for antibiotics
7)Provide attachment to complement
Difference Gram positive Gram negative
1. Thickness 15-25 nm 10-15 nm
2. variety of amino acid Few Several
3. aromatic & sulfar containing
4. Lipid Low 2-4 % High 15-20 %
5. Teichoid acid Present Absent
6. Periplasmic space Absent Present
7. result of enzyme digestion Protoplast Spheroplast
Absorb stain appear purple
Don’t absorb stain appear
The type of cell wall is used by
doctors to help diagnose disease
The bacteria are stained with a
special stain called Gram stain
Bacteria without the extra membrane,
appear purple. These are Gram positive
(Gram +) bacteria
bacteria with the extra membrane
appear pink. These are Gram negative
( Gram -) bacteria
“thin semipermiable membrane which lies
just beneath the cell wall that is called as cyto
The whole bacterial cytoplasm is bound
peripherally by very thin,elastic and
semipermiable cytoplasmic membrane also
known as cell membrane.
It is 5-10nm in width
Electron microscope shows the presence of three
layer constituting a unit membrane structure.
Chemically the membrane consist of
phospholipid with small amount of protein.
Sterol is absent except in mycoplasma.
The seperation of membrane from cell wall is
achived by readily in gram negative bacteria
when they are suspended in medium of high
osmotic tension.such phenomenom is called as
(1) Active transport:
it is site of numerous enzymes (oxidase
polymerase, permease) involved in the active
transport of selective nutrients. It is
impermiable to macromolecule nd ionised
(2) Passive transport:
It is act as semipermiable membrane
through inward and outward passage of water
and passive trnsport of molecule lipid soluble
solutes take place by diffusion
it is also concentration sugar, amino acids
and phosphate so that a 300-400 fold grandient
exists across osmotic barrier.
(3) Enzymatic function:
it also contain cytochrome oxidase, enzyme
of tricarboxylic acid cycle and polymerising
enzyme necessary for synthesis of cell wall
“Bacterial cytoplasm is
suspension of organic and inorganic
solutes in viscous watery solution”
It is not exhibiting protoplasmic streaming
and it lacks endoplasmic reticulum or
mitochondria. It contains ribosomes,
mesosomes, inclusion and vacuoles.
All the organills which cytoplasm contains
is as follows.
Ribosomes appear as small granules and pack
the whole cytoplasm. These are strung together
on strands of mRNA to form polymers.
the code of mRNA is translated in to peptides
sequence t this place.
The ribosomal particles become linked up and
travels along the mRNA strand.
Site for protein synthesis.
They are the group of ribosomes linked
together like beads of chain by messanger RNA
They are vesicular, convulated or
multilaminted structures formed as invagination
of plasma membrane in cytoplasm .
They are more prominent in the gram positive
Two types of mesosomes
(a) septal mesosomes:
It is attached to bacterial chrosome nd involved in
dna segregation and in formation of cross wall during cell
(2) Lateral mesosomes:
They are at lateral side
They are site of respiratory enzymes
Coordinate nuclear and cytoplasmic membrane division
during binary fission
Responsible for compartmenting DNA at sporulation
“ It is an outer covering of thick jelly like
material that surrounds the bacterial cell wall”
Width: 0.2 micrometer
Contains about 90% water and 2% solid
The solid constitutes may be complex
polysccharide (pneumococcus klebsiella,
enterobacter) or polypeptides (anthrax bacillus)
or hyaluronic acid (streptococcus)
the capsule is best seen in pathological
specimens like pus, blood, sputum, and exudates
(1) By ordinary stain (gram or acid fast) capsule
can not be stained, it apper as halo arround the
stained bacterial body.
(2) In negative staining (india pink preparation),
capsule appears as clear halo around the
bacterium as link can not penetrate capsule.
Immunological method: in that stained
with antiserum that swallowed by capsule
so it appear as swollen under microscope
so it is called as capsular awelling
reaction. E.g pneumococcus
Capsule serve as protective covering
against antibacterial substances such as
bacteriophase, phagocytes and enzymes
Enhance bacterial virulance
Capsular antigen is hapten in nature and
specific for bacteria.
“These are long, sinnous contractile
filamentous appendages known as f lagella”.
Composed of a flagellin subunit.
Usually sheathed (covered).
Rotates by way of a basal body in the
Unique to bacteria.
These are organs of locomotion . ex:-Escherichia
coli salmonella, vibrio , pseudomonas, etc.
The number of f lagella varies up to 10 to 20 per
cells according to species of bacteria.
These are extremely thin (diameter)12 to 30 nm,
helical shaped structure of uniform diameter
throughout their length .
these are 3 to 20 nm long.
Each flagellum consist of hook & basal body. It
originates in a spherical body located just inside
Composed of filament, hook, and basal body
Flagellin protein (filament) is deposited in a helix
at the lengthening tip
Base of filament inserts into hook
Basal body anchors filament and hook to cell wall
by a rod and a series of either two or four rings of
Filament capable of rotating 360º
Monotrichous; 1 flagella
Lophotrichous; tuft at one end
Amphitrichous; both ends
Peritrichous; all around bacteria
It is responsible for bacterial motility.- Motility
may be observed microscopically or by
detecting the spreading growth in semi solid agar
Dark ground microscopy.
Special staining techniques in which their
thickness is increased by mordanting.
Hanging drop preparation.
“Fimbria are filamentous , short , thin , straight , hair
This is 0.1 to 1.5 µ long & less than 4 to 8 nm thick.
They are also called as Pili.
Fimbriae are seen only in some gram negative bacteria.
Each bacterium may have 100 to 500 Fimbriae on all
over the body of bacteria.
They project from cell surface as a straight filaments.
They are best developed in freshly isolated strains & in
They are composed of protein known as pillin (molecular
weight 18000 Daltons).
Different forms of fimbria –
ii)F (fertility) pili
iii) Col I (colicin)pili
Fimbriated bacteria form pellicle in liquid
a) Organ of adhesion.
b) Hem agglutination.
c) They are antigenic.
d) Agglutination & pellicle formation.
e) Genetic material is transferred from the
donor to recipient cell.
1 Size larger & thicker Smaller & thinner
2 Arise from cytoplasm or cytoplasmic membrane but
does not attached to cell wall
Attached to cell wall
3 Organ of movement (locomotion) Organ of adhesion &
4 They are never straight They are alwase strait
“ spores are highly resistant dormant stage of
bacteria formed in unfavourble environmental
condition such as starvation and dessication”
As spores are formed within the parent bacterial
cell so they are also called as endospores
During germination each spore give rise to only
one vegetative bacteria
Exospores found in fungi(conidia) formed
extracellularly from end of parent cells.
Sporulation is not a method of reproduction
A. Gram positive bacilli:
(1) obliterate aerobic- genus bacillus.e.g
(2) obliterate anaerobic:genus clostridia.e.g
C.tetani, C.welchii, C.botulism
B. Other bacteria:
Gram positive coccus (porosarcina) gram
negative bacilli (coxiella burnetii)
The cell membrane grows inward and forms
spore wall around the core (forespore). The
inner-most layer of the spore wall forms the
spore membrane from which the cell wall of
future vegetative bacterium develops. Outside
this membrane is thick layer, the cortex and a
multilayered tough spore coat. Some spores
have an additional apparently rather loose,
outercovering called exosporium.
spontaneous sporulation occurs in
condition unfavourable condition such as
starvation, dessication, presence of
disinfectants and in extreme temperature.
Spore formation is initiated by apperance of clear area in
portion of protoplasm near one end of bacterial cell and
that protoplasm gradually become more opaque that form
The cell membrane grow inwards and undergoes infolding
forming double layered membrane structure around the core
The inner most layer of spore wall forms spore membrane in
future vegetative bacterium will develop. The spore wall
synthesis a thick covering lyer cortex and multilayered thin
but tough outer layer spore coat
Spores of some spesis have additional apparently
rather loose outer covering called exosporium
Spore cortex contains unusual type of peptidoglycan
sensetive to lysosomes the spore cot is made up of keratin
which is impervious to antibacterial chemical agent
Exosporium is a lipoprotein membrane with some
carbohydrate residue. Young spores remain attached to
The young spore remain attached t parant
cell. The precise position and shape and
relative size of spores remain constant within
Spore may be central,sub terminal or
Bacterial spores are resistant to ordinary boiling,
heating, and disinfectant. They can withstand
boiling up to 3 hr, dry heat at 150c for 1 hr
however they are destroyed by autoclaving at
121c for 15-20 min.
The highly impervious spore coat, low water
content, low metabolic activity and high
concentration of calcium dipicolinate of spore
make resistant to drying and heat.
“ The process of conversation of spore in
to vegetative cell under suitable environment is
known as germination”
There are three stages of germination
The germintion of bacterial spore do not
occur even when placed in environment that
Unless first activated by one or onother
agent damage the coat of spore such as heat,
abration and compound containing free
The process of initiation is not clear,
however the spore will initiate germination
in favourable condition.
Different species of bacteria recognizes
different effactors as signalling a rich
medium such as L-alanine for one spesis
With the swelling of spore wall and
disintegration of cortex a single germ cell
emerge after breaking open the spore coat.
The new vegetative cell consist of spore
protoplast with its surrounding wall.
Formation of vegetative cell.
By ordinary stain and modified Z-N stain.
for making sterilization
Pili – hairlike structures usually found
in Gram neg. bacteria. Help the
bacteria stick to surfaces.
Also forms conjugation bridge
Chromosome – a single loop of DNA
that is folded on itself
- controls the cell’s function
Nucleoid – the region of the cytoplasm
where the DNA is found
Plasmid – an accessory loop of DNA – small contains only a few
genes - can be responsible for: conjugation, antibiotic
resistance, unique metabolic properties – like the ability
to use hydrocarbons
Capsule – found outside some bacteria stores nutrients and protects
the bacteria from changing environmental conditions
Short protein appendages
smaller than flagella
Adhere bacteria to surfaces
E. coli has numerous types
K88, K99, F41, etc.
Antibodies to will block adherance
F-pilus; used in conjugation
Exchange of genetic information
Flotation; increase boyancy
Pellicle (scum on water)
More oxygen on surface