1-Bacterial Morphology

Bacterial Morphology
Dr. Abdulaziz Al-Khattaf

Protoplasm
• Bacteria organized in units
known as cells. Cells are
composed of a body
protoplast, enclosed by a
thin semi-permeable
membrane, cytoplasm and
a cell-wall.
• Bacteria are microscopic
living forms, simple
(Prokaryotes) and
unicellular in structure.
• Bacteria can grow in
nutritive solid media to
form colonies that are
visible to the naked eye.
• Prokaryotic cells (Bacteria, Rickettsiae,
Chlamydiae and Mycoplasma) distinguishing
features are:
– Nucleus is homogeneous body with no
nuclear membrane- separating it from
cytoplasm.
– Lacks internal membranes isolating the
respiratory and photosynthetic enzymes
systems in the specific organelles.
– Contains a rigid peptidoglycan cell-wall for
support and protection.
Bacterial shapes
• Due to cell-wall
presence bacteria could
be in spherical (coccus),
rod-shaped (bacillus),
comma-shaped (vibrio),
spiral (spirochaete) or
filamentous.
Bacterial Structure
• Protoplast: the whole body of living material.
• Cytoplasmic membrane: holding and containing the
protoplast.
• Cell wall: outside rigid supporting the cell (porous-
relatively permeable).
• Cytoplasm: consist of watery sap containing
ribosomes, mesosomes and chromatin.
• Inclusion granules: for storage products such
aspolyphosphate, lipids and starch.
• Capsule: protective gelatinous covering
layer.
• Flagella: filamentous organs of
locomotion.
• Fimberiae: organs of adhesion.
• Pili: involve in the transfer of genetic
material.
• Bacterial DNA:
• Genetic information of bacterial cell contained
in a single, circular double-stranded DNA.
• DNA undergoes semi-conservative replication.
• Cytoplasm of bacteria:
• A viscous watery solution, containing organic
and inorganic solutes and ribosomes.
• Ribosomes:
• They are distributed throughout the
cytoplasm and are the sites of protein
synthesis.
• On the ribosomes subunits (30S and 50S), the
mRNA would form peptide sequences.
• Transfere RNA (tRNA) molecules would built
the peptide sequences into specific
polypeptides.
• Cytoplasmic inclusions:
• Volutin granules (metachromatic granules)

Source of stored energy (polymetaphosphate),
found in diphtheria bacillus with methylene blue
dye or with Albert and Neisser staining.
• Lipid-granules: act as carbon and energy storage
product.
• Polysaccharide granules: either starch or
glycogen.
Spores
• Spores produced by bacteria in the genera
Bacillus and Clostrridium enable them to survive
hard environment conditions.
• Spores are developed within of vegetative cells.
• Spores are resistant to heat, desiccation and
disinfectants.
• Spores are described as terminal, sub-terminal
or central.
Cell Wall
• Cell-wall provides rigidity and protects bacterial
cell against osmotic damage.
• Porous and permeable to substances of low
molecule weight.
• Structure of cell-wall differs in Gram-positive
and Gram-negative.
• Gram-negative cell contains an outer membrane
with specific proteins that form porins.
Cell Wall
• Through these porins hydrophilic molecules are
transported.
• Other proteins are receptor sites for phages and
bacteriocins.
• Lipopolysaccharide O antigens and lipid
(endotoxin) are embedded in the outer
membrane.
• Gram-positive cell wall has much thicker layer of
peptidoglycan than gram-negative cell-wall.
• Teichoic acids are part of the cell wall of gram
positive bacteria. They maintain divalent cation
outside the cytoplasmic membrane.
• Bacteria can survive with defective cell-walls
and this was demonstrated in the laboratory
with the presence of antibiotics and
hyperosmatic environments.
• Mycoplasma: independent bacterial genus lacks
cell-wall.
• L-forms: bacteria with wall-deficient result of
penicillin treatment. Can survive and replicate
on ordinary media.
External structures
• Flagella: Helical filaments, which produce
motility by rotation.
– Monotrichous is a single polar flagellum;
lophotrichous has two or more polar flagella
at one end of the cell; amphitrichous has a
single flagellum at each end of the cell; and
peritrichous with flagella distributed over
the cell.
– A flagellar protein (H antigen) is useful for
helping distinguish between serotvars
(serotypes) or variation within a species.
External structures
• fimbriae and Pili: many bacteria cells have
numerous hairlike structure (fimbriae) that
are shorted than flagella.
• Fimbriae help the cell to adhere to surfaces
such as mucous membranes.
• They are often a factor in pathogenicity.
• Pili: are les in number than fimbriae (one or
two) and called sex pili –they function in
transfere of DNA from one cell to another.
External structures
• capsules: amorphous (formless) material which

surrounds many bacterial species as their
outermost layer.
• Usually polysaccharide, occasionally protein.
• Usually inhibit phagocytosis and their presence

correlates with virulence in certain bacteria.
Bacterial Staining
• Staining simply coloring the microorganism with
dye that emphasizes certain structures.
• Fixing (attaching) bacteria to the slide is the first
step.
• Stains are salt compose of a positive or negative
ions. Basic dyes, are positively ion charged
where, in acidic dyes, negatively ion charged.
• Bacteria cell is slightly negatively charged so
attracting basic dyes (crystal violet, methylene
blue, malachite green, and safranin).
Bacterial staining
• Acidic dyes: are not attracted to bacteria
because of its negative charge that repelled
by the bacterial negative charge.
•
• This stain colors the background instead
(negative staining).
•
• This is useful to observe the over all cell
shape, sizes and capsules (eosin, acid fuchsin
and nigrosin).
Colonies appearance

1-Bacterial Morphology

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Bacterial Morphology

Dr. Abdulaziz Al-Khattaf

• Volutin granules (metachromatic granules)

• capsules: amorphous (formless) material which

• Usually polysaccharide, occasionally protein.

• Usually inhibit phagocytosis and their presence

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