Microbiology is the study of the biology of microscopic organisms - viruses, bacteria, algae, fungi, slime molds, and protozoa. The methods used to study and manipulate these minute and mostly unicellular organisms differ from those used in most other biological investigations

2. Learning Objectives
After reading and studying this chapter, you should be
able to:
♦ Differentiate between prokaryotes and eukaryotes.
♦ Describe anatomy of bacterial cell.
♦ Describe cell envelope.
♦ Describe bacterial cell wall.
♦ Discuss capsule or bacterial capsule.
♦ Describe bacterial flagellae.

3. ♦ Describe fimbriae or pili.
♦ Discuss bacterial spores or endospores.
♦ Explain L-forms of bacteria.

4. ♦ Living material is organized in unit and
microorganism were living form of microscopical size
and usually unicellular in structure originally
organization is unsatisfied.

5. 3

6. Bacterial Cell

7.  Unicellular
 Circular DNA
 No organelles
 1/10th the size of eukaryoticcells
 Flagella-long hair-like structure used for movement
 Reproduce asexually –Binary Fission

8.  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
width
 The limit of resolution with unaided eye is about
200 u because of that bacteria can be only
visualized under microscope.

9. Depending on their shape, bacteria are classified into
several varieties :
1. Cocci: Cocci (from kokkos meaning berry) are
spherical, or nearly spherical.
2. Bacilli: Bacilli (from baculus meaning rod) are
relatively straight, rod shaped (cylindrical) cells. In
some of the bacilli, the length of the cells may be equal
to width. Such bacillary forms are known as
coccobacilli and have to be carefully differentiated from
cocci.
Shape of Bacteria

10. 3. Vibrios: Vibrios are curved or comma-shaped rods
and derive the name from their characteristic vibratory
motility.
4. Spirilla: Spirilla are rigid spiral or helical forms.
5. Spirochetes: Spirochetes (from speira meaning coil
and chaite meaning hair) are flexuous spiral forms.

11. 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

13. • In the bacteria the outer layer or cell envelop or
bacteria consist of two things
(a) rigid cell wall
(b) underlying cytoplasmic membrane or
plasma membrane:
it includes granules, ribosomes,
mesosomes and circular DNA.

14.  Some bacteria in addition to possess additional
structures such as gelatinous material which
cover it is called as capsule and when it is too
thin it is called as microcapsule.

15.  Flagella
 Pili
 Capsule
 Plasma Membrane
 Cytoplasm
 Cell Wall
 Lipopolysaccharides
 Teichoic Acids
 Inclusions
 Spores
Chapter 4

17.  Introduction:
most
consisting of
cell
cell
posses a cell envelop
wall and underlying
cytoplasmic membrane.
 Definition:
“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
wall

18. 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
 N-acetylglucosamine
 N-acetymuramic acid
 Amino acids cross link NAG & NAM

19. cell
membrane
 Made of peptidoglycan – a combination of protein and
polysaccharides
 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
bacteria
cell wall
cell
membrane
Outer membrane
lipopolysaccharide
cell wall

21.  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)

22.  Periplasmic space : it is the space between
inner & outer membrane which contains
important proteins and oligosaccharides.

23. 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.

24.  Function
 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
environment.
 6) contains receptor sites for antibiotics
 7)Provide attachment to complement

25. Gram positive Vs gram negative

28. Difference Gram positive Gram negative
1. Thickness 15-25 nm 10-15 nm
2. variety of amino acid Few Several
3. aromatic & sulfar containing
amino acid
Absent Present
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

29. Absorb stain appear purple
Don’t absorb stain appear
pink
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

31.  Definition:
“thin semipermiable membrane which lies
just beneath the cell wall that is called as cyto
plasmic membrane”
 The whole bacterial cytoplasm
peripherally by very thin,elastic
membrane
is bound
and
also
semipermiable cytoplasmic
known as cell membrane.
 It is 5-10nm in width
 Electron microscope shows the presence of three
layer constituting a unit membrane structure.

32.  Chemically
phospholipid
the membrane consist of
with small amount of protein.
Sterol is absent except in mycoplasma.
 DEMONSTRATION:
 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
plasmolysis
 Electron microscope

36.  Transport:
(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
substances.
(2) Passive transport:
It is act as semipermiable membrane
through inward and outward passage of water
and passive transport of molecule lipid soluble
solutes take place by diffusion

37. (2) Concentration:
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

38. “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.

39. (1) Ribosomes:
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.
Function:
Site for protein synthesis.

40.  Polysomes:
They are the group of ribosomes linked
together like beads of chain by messanger RNA
 Mesosomes:
They are vesicular, convulated or
multilaminted structures formed as invagination
of plasma membrane in cytoplasm .
They are more prominent in the gram positive
bacteria.

41.  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 division.
(2) Lateral mesosomes: They
are at lateral side
Functions:
 They are site of respiratory enzymes
 Coordinate nuclear and cytoplasmic membrane division
during binary fission
 Responsible for compartmenting DNA at sporulation

42. “ 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
polysccharide (pneumococcus
complex
klebsiella,
enterobacter) or polypeptides (anthrax bacillus)
or hyaluronic acid (streptococcus)

43.  Demonstration:
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.

44.  Immunological method: in that stained with
antiserum that swallowed by capsule so it appear
as swollen under microscope
awelling
so it is called as capsular
reaction. E.g pneumococcus
 Capsulated organism:
s.pneumoniae,Bacillus anthracis,
C.perfringes, pneumobacillus,
H.influenzae

45.  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.

46.  Definition
 “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
bacterial cell.
 Unique to bacteria.

47.  These are organs of locomotion . ex:-Escherichia
coli salmonella, vibrio , pseudomonas, etc.
 The number of flagella 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
cell wall.

48. 43

49.  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
integral proteins
 Filament capable of rotating 360º

50.  Arrangement/ types
 Monotrichous; 1 flagella
 Lophotrichous; tuft at one end
 Amphitrichous; both ends
 Peritrichous; all around bacteria

52. Function
 It is responsible for bacterial motility.- Motility may
be observed microscopically or by detecting the
spreading growth in semi solid agar medium.
Demonstration –
 Dark ground microscopy.
 Special staining techniques in which their thickness is
increased by mordanting.
 Electron microscop.
 Hanging drop preparation.

53.  Definition
 “Fimbria are filamentous , short , thin , straight , hair
like appendage”.
 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.

54.  They are best developed in freshly isolated strains
& in liquid culture.
 They are composed of protein known as pillin
(molecular weight 18000 Daltons).
Different forms of fimbria –
 i)common pili
 ii)F (fertility) pili
 iii) ColI (colicin)pili

55. DEMONSTRATION:-
 Electron microscop.
 Hem agglutination.
 Fimbriated bacteria form pellicle in liquid media.
FUNCTION:-
 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.

56. Sr.n
o
Flagella Fimbriae
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 &
conjugation
4 They are never straight They are alwase strait

57. “ 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

58. A. Gram positive bacilli:
(1) obliterate aerobic- genus bacillus.e.g
B.anthracis, B.subtilis
(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)

60.  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
have an additional apparently rather
multilayered tough spore coat. Some spores
loose,
outercovering called exosporium.

62. spontaneous sporulation occurs in
condition unfavourable condition such as
starvation, dessication, presence of disinfectants
and in extreme temperature.

63. 58
http://www.microbe.org/art/endospore_cycle.jpg

64. 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
forespore
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

65. 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
with some
attached to
Exosporium is a lipoprotein membrane
carbohydrate residue. Young spores remain
parent cell

66.  The young spore remain attached t parant cell.
The precise position and shape and relative size
of spores remain constant within particular
bacteria.
 Spore may be central,sub terminal or terminal

67.  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.

68.  Definition:
“ The process of conversation of spore in to
vegetative cell under suitable environment is
known as germination”
There are three stages of germination

69.  The germintion of bacterial spore do not occur
even when placed in environment that favour
process.
 Unless first activated by one or onother agent
damage the coat of spore such as heat, abration
and compound containing free sulphydryl
groups.

70.  The process of initiation is not clear, however
the spore will initiate germination in
favourable condition.
 Different
different
species
effactors
of bacteria recognizes
as signalling a rich
medium such as L-alanine for one spesis

71.  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.

72.  By ordinary stain and modified Z-N stain.
 Laboratory:
for making sterilization

73. Chapter 4

74.  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

75.  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

76. Chapter 4