MORPHOLOGY OF
BACTERIA
DR.RUPAL PATEL
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Kingdom : PROTISTA
Prokaryotes :evolutionarily ancient. first and for billions of
years ,only form of life..
Pro = “before”, karyon = “nucleus”
Prokaryotes :
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Prokaryotes most always single-celled,.
Lack a membrane bound nucleus.
Genetic material naked within the cytoplasm,
Ribosomes their only type of organelle.
Nucleoid region of cytoplasm where chromosomal DNA is
located, usually a singular, circular chromosome.
Reproduce by means of binary fission, duplicating their genetic
material and then essentially splitting to form two daughter cells
identical to the parent.
Bacteria (including the blue green "algae") are prokaryotes.
Higher organisms together with microorganisms such as
fungi, protozoa are eukaryotes.
PROKARYOTES VERSUS EUKARYOTES
PROKARYOTES
EUKARYOTES
a) Size
1-10 microns
10-100 microns
b) Complexity
unicellular, rarely small clusters
or filaments
sometimes unicellular more often
multicellular
c) Membrane bound
organelles
none (mesosome is infolding of
cytoplasmic membrane)
nuclei, mitochondria, chloroplasts,
lysosomes, endoplasmic reticulum,
golgi, & vacuoles
d) Nucleus
no
yes
e) Chromosomes
single & circular
usually several & linear
f) Mitosis & Meiosis
absent
present
g) Endocytosis & cytoplasmic
streaming
absent
present
h)Sterols
usually absent
used as hormones and in plasma
membrane
SHAPES OF BACTERIA
 Coccus
Chain = Streptoccus
 Cluster =
Staphylococcus
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 Bacillus
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Chain =
Streptobacillus
 Coccobacillus
 Vibrio
= curved
 Spirillum
 Spirochete
COCCUS:
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The cocci are spherical or oval bacteria having
one of several distinct arrangements:
BACILLUS:
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Bacilli are rod-shaped bacteria. They divide in one
plane producing one of the following:
SPIRAL:
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A helical or corkscrewshaped bacterium.
Spirals come in 1 of 3
form
Vibrio: curved or commashaped rod
Spirillum: thick, rigid spiral
Spirochete: thin, flexible
spiral
BACTERIAL STRUCTURES
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Cell Wall
- Lipopolysaccharides
-Teichoic Acids
Plasma Membrane
 Cytoplasm
 Flagella
 Pili (fimbria)
 Capsule
 Inclusions
 Spores
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CELL WALL
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20-40% of bacteria
Unique structure which surrounds the cell membrane.
Not present in every bacterial species
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Functions :
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-Maintaining the cell's characteristic shape
-Countering the effects of osmotic pressure
-Providing attachment sites for bacteriophages- teichoic acids
attached to the outer surface of the wall are like landing pads for
viruses that infect bacteria
-Providing a rigid platform for surface appendages- flagella,
fimbriae, and pili
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Some antibiotics effect directly
 Penicillin
CELL WALL
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Peptido-glycan Polymer (amino acids +
sugars)
Sugars; NAG & NAM
- N-acetylglucosamine
- N-acetymuramic acid
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D form of Amino acids used
The peptidoglycan polymer is composed of an
alternating sequence of N-acetylglucosamine and Nacetyl-muraminic acid.
Each peptidoglycan layer is connected, or cross linked,
to the other by a bridge made of amino acids and amino
acid derivatives.
The cross linked peptidoglycan molecules form a
network which covers the cell like a grid.
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The cell walls of all bacteria are not identical.
Cell wall composition is one of the most
important factors in bacterial species analysis
and differentiation.
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are two major types of walls:
-Gram-positive and Gram-negative.
Gram-positive bacteria
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Many polymer layers of peptidoglycan
connected by amino acid bridges.
90% of the Gram-positive cell wall is comprised of
peptidoglycan.
TEICHOIC ACIDS
-Glycerol, Phosphates, & Ribitol
-Attachment for Phages
Gram-negative bacteria
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Much thinner, only 20% peptidoglycan.
Two unique regions
A) Periplasmic space
- separates the outer plasma membrane from the peptidoglycan
layer.
- contains proteins which destroy potentially dangerous foreign
matter present in this space.
B) Lipopolysaccharide layer(LPS)
- Located adjacent to the exterior peptidoglycan layer.
- Phospholipid bilayer attached to the peptidoglycan by
lipoproteins.
-The lipid portion of the LPS contains a toxic substance, called
Lipid A, responsible for most of the pathogenic affects associated
with harmful Gram-negative bacteria.
-Polysaccharides extend out from the bilayer contibute to the
toxicity of LPS.
The LPS, lipoproteins, and the associated polysaccharides
together form what is known as the outer membrane
LPS (CONT’D)
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Functions
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Toxic:
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Gm -ve septicemia; death due to LPS
Pyrogen; causes fever
Heat Resistant; hard to remove
 Acetone or alcohol can remove
 O Antigen of Salmonella and E. coli
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2,000 different O Ags of Salmonella
 100’s different O Ags of E. coli
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E. coli O157
CYTOPLASMIC MEMBRANE :DELICATE AND PLASTIC STRUCTURE
THAT COMPLETELY ENCLOSES THE CELL CYTOPLASM (OR PROTOPLASM)
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Made up of a phospholipid bilayer
Proteins are embedded in the
membrane.
-TRANSPORT proteins that
BIND specific molecules and carry
them into or out of the cell as
required.
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These proteins are held in the
membrane by virtue of hydrophobic
and hydrophilic regions on the
protein.
Contains enzymes involved in
cellular respiration, peptidoglycan
biosynthesis
CYTOPLASM
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Colloidal system containing organic and
inorganic solutes in a viscous watery solution
Ribosomes :
-protein synthesis
-slightly smaller than eukaryotic cells (70 S)
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Mesosomes :
-vesicular, convoluted or multilaminated structures
- site of the synthesis of cross wall septa
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Intracytoplasmic inclusions
- volutin granules present in Diptheria bacilli
NUCLEUS
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No nuclear membrane
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Genome :single , circular ,double stranded DNA
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Extra nuclear genetic elements : Plasmids
- transferred from one bacterium to another either
through conjugation or through bacteriophages
- confer properties like toxigenecity and drug resistance
FLAGELLA
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Flagella are whip-like structures protruding from the
bacterial cell wall and are responsible for bacterial motility
(i.e. movement).
Long (3 to 12 µm), diameter about 12-30 nanometers
The protein subunits of a flagellum are assembled to form a
cylindrical structure with a hollow core.
Immunogenic
Constitute a group of protein antigens called the H
antigens, which are characteristic of a given species, strain,
or variant of an organism.
Antigenic changes of the flagella known as the phase
variation of H1 and H2 occurs in Salmonella typhimurium
A flagellum consists of three parts:
(1) long filament, which lies external to the cell surface;
(2) hook structure at the end of the filament;
(3) basal body, to which the hook is anchored with series of rings
that drive the flagella. and which imparts motion to the flagellum.
Typical arrangements of bacterial flagella
DETECTING BACTERIAL MOTILITY
1. Flagellar stains : outline flagella and show their pattern of
distribution. If a bacterium possesses flagella, it is presumed to
be motile.
2.Motility test medium :.
-Semisolid medium (0.5 % - 0.75% agar ) inoculated with bacteria in a
straight- line stab.
-After incubation : turbidity (cloudiness) due to bacterial growth away
from the line of the stab : bacteria able to swim through the medium.
3. Direct microscopic observation in a wet mount.
-Brownian movement, due to random collisions between water
molecules and bacterial cells.
-True motility ,bacterium swim from one side of the microscope field
to the other side.
FIMBRIAE
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AND
PILI
Fimbria :
-protein tubes that extend out from the outer membrane.
-generally short in length
-present in high numbers about the entire bacterial cell
surface.
-facilitate the attachment of a bacterium to a surface (e.g.
to form a biofilm) or to other cells (e.g. animal cells during
pathogenesis).
Pili :
-similar in structure
-much longer
-present on the bacterial cell in low numbers.
-involved in the process of bacterial conjugation.
Fimbriae (common pili) and flagella on the surface of bacterial cells.
Left: dividing Shigella enclosed in fimbriae. The structures are probably
involved in the bacterium's ability to adhere to the intestinal surface.
Right: dividing pair of Salmonella displaying both its peritrichous flagella
and its fimbriae. The fimbriae are much shorter and slightly smaller in
diameter than flagella.
CAPSULES AND SLIME LAYERS
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A true capsule : Discrete
detectable layer of
polysaccharides deposited
outside the cell wall. Sharply
defined.
Slime layer (biofilm ):A less
discrete structure or matrix
which embeds the cells .Loose
undemarked secretion
Glycocalyx or microcapsule:
very thin layer of tangled
polysaccharide fibers on the cell
surface.
Generally composed of
polysaccharides; rarely they contain
amino sugars or peptides.
FUNCTIONS
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Adherence of cells to surfaces.
Protect bacterial cells from engulfment by protozoa or
white blood cells (phagocytes)
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Protect from attack by antimicrobial agents
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protect cells from effects of drying or desiccation.
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Ability to block some step in the phagocytic process so
prevent the bacterial cells from being engulfed or destroyed
by phagocytes (white blood cells).
-Streptococcus pneumoniae (lobar pneumonia)
-Bacillus anthracis (anthrax)
-Neisseria meningitidis (meningitis
SPORE
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Endospores are highly heat-resistant, dehydrated resting cells
formed intracellularly in members of the genera Bacillus and
Clostridium.
Sporulation, the process of forming endospores, is an unusual
property of certain bacteria.
The process, usually begins in the stationary phase of the
vegetative cell cycle, is initiated by depletion of nutrients
(usually readily utilizable sources of carbon or nitrogen, or both).
The cell then undergoes a highly complex, well-defined sequence
of morphologic and biochemical events that ultimately lead to the
formation of mature endospores.
Structure of a bacterial endospore, renowned as the
most durable and long-lived type of cell on earth
The cross section of a bacterial spore, such as anthrax, shows
its hard, multilayered coats, which both make the spore difficult
to kill and allow it to remain dormant for many years.
The cycle of spore formation and germination
At the beginning of spore formation, a septum forms, separating the nascent spore
from the rest of the cell and all of the genetic material of the cell is copied into the
newly-forming cell.
The spore contents are dehydrated and the protective outer coatings are laid down.
Once the spore is matured it is released from the cell.
On germination, the spore contents rehydrate and a new bacterium emerges and
multiplies.
SPORE STRUCTURE AND ARRANGEMENTS.
General structure of a bacterial
Endospore
A = oval, terminal;
B = rectangular, terminal;
C = rectangular, subterminal,
D = rectangular, central;
E = circular, terminal;
F = circular, central;
G = terminal, club-shaped.