MPS 206 Bacteriology Lecture 3 and 4 Notes.pptx

BACTERIAL STRUCTURE, MORPHOLOGY
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MEDICAL BACTERIOLOGY

BACTERIA
• Bacteria are microscopic, single-celled organisms
that thrive in diverse environments.
• These organisms can live in soil, the ocean and
inside the human gut.
• Bacteria represent a large and diverse
group of microorganisms that can exist as
single cells or as cell clusters.
• Some bacteria are harmful, but most serve a useful
purpose.
• They support many forms of life, both plant and
animal, and they are used in industrial and
medicinal processes.

Bacteria Cont’d
• Bacteria are thought to have been the first
organisms to appear on earth, about 4 billion years
ago.
• A gram of soil typically contains about 40
million bacterial cells.

STRUCTURE OF BACTERIA
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• Smaller and simpler in
structure
than
eukaryotic cells, with no
recognizable organelles.
• All of the activities performed by
organelles also take place in bacteria, but
they are not carried out by specialized
structures.
• The small size, simple design, and
broad
metabolic capabilities of bacteria allow them
to grow and divide very rapidly and to
inhabit and flourish in almost any
environment.

STRUCTURE OF BACTERIA
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• They were first seen under a microscope by
Anton
van Leeuwenhoek in 1676.
• As microscopes have improved, scientists
have
come to understand bacterial cell structure
better.

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Bacterial cell structure
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Organized into 3 categories :
• Internal Structures: Cytoplasm, nucleoid, bacterial
chromosome, plasmid, ribosomes, and storage
granules
• Cell envelope: cell membrane, peptidoglycan cell wall or
an outer lipid membrane (only found in Gram-negative
cells)
• External structures (appendages & coverings):
flagella, fimbriae, sex pilus and capsule (glycocalyx)
and sometimes spores (in some bacteria)

Intracellular structures
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• Cytoplasm
• Chromosome
• Plasmid
• Ribosomes
• Inclusion
bodies

Cytoplasm
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• Portion of the cell that lies within the PM
• substances within the plasma membrane,
excluding
the genetic material.
• Gel-like matrix composed of mostly water(4/5
th ), enzymes, nutrients, wastes, and gases
• Contains cell structures - ribosomes, chromosome,
and plasmids , as well as the components
necessary for bacterial metabolism.
• It is relatively featureless by electron microscope
- although small granules can be seen.
• carries out very important functions for the cell -
growth, metabolism, and replication .

Constituents
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– Proteins including enzymes
– Vitamins
– Ions
– Nucleic acids and their precursors
– Amino acids and their precursors
– Sugars, carbohydrates and their
derivatives
– Fatty acids and their derivatives

Nucleoid
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• Unlike the eukaryotic (true) cells, bacteria do not
have a membrane enclosed nucleus.
• The nucleoid is a region of cytoplasm where the
chromosomal DNA is located.
• It is not a membrane bound nucleus, but simply
an area of the cytoplasm where the strands of
DNA are found.

Plasmids
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• small extra-chromosomal DNA
• contain genes for antibiotic resistance or virulence.
• Structure Similar to most bacterial chromosomes,
but considerably smaller.
• plasmids are covalently closed circular DNA
• In a few species linear plasmids have been found.
• Size : Chromosomal DNA is typically about 4000 kb,
• plasmid DNA ranges from 1-200 kb.
• Number of plasmids: 1-700 copies of plasmid in
a cell.

Plasmid Function
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• The function of plasmids is not always known, but they
are not normally essential for survival of host,
although their presence generally gives the host some
advantage.
• Antibiotic resistance - Some plasmids code for
proteins
that degrade antibiotics-a big advantage for
pathogens.
• Some encode for proteins which confer virulence
factors on the host. For example- E. coli plasmid
Ent P307 codes for an enterotoxin which makes E.
coli pathogenic.
• Conjugative plasmids - These allow exchange of
DNA between bacterial cells.

Plasmids
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• Plasmids and the associated traits can be
transferred between bacteria, even from one
bacterial species to another.
• Plasmids are not involved in reproduction.
• Plasmids replicate independently of the
chromosome.
• Plasmids are passed to other bacteria by two
means.
• For most plasmid types, copies in the cytoplasm are
passed on to daughter cells during binary fission.

Plasmids
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• Other types of plasmids ,form 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.
• Plasmids have been shown to be instrumental in
the transmission of special properties, such as
antibiotic drug resistance, resistance to heavy
metals, and virulence factors necessary for
infection of animal or plant hosts.
• The ability to insert specific genes into plasmids
have made them extremely useful tools in the
area of genetic engineering/RDNA Technology .

Ribosomes- protein synthesis
machinery
• Consists of RNA and protein
• Abundant in cytoplasm
• Often grouped in long chains called polyribosomes.
• give the cytoplasm of bacteria a granular
appearance in EM.
• smaller than the ribosomes in eukaryotic cells-
but have a similar function
• Bacterial ribosomes have sedimentation rate of
70S;
their subunits have rates of 30S and 50S.
• The unit used to measure sedimentation velocity
is Svedberg BACTERIAL STRUCTURE, MORPHOLOGY
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Ribosomes
• They translate the genetic code from the molecular language of
nucleic
acid to that of amino acids—the building blocks of proteins.
• Bacterial ribosomes are similar to those of eukaryotes, but are smaller
and have a slightly different composition and molecular structure.
• Bacterial ribosomes are never bound to other organelles as
they sometimes are bound to the endoplasmic reticulum in eukaryotes,
but are free-standing structures distributed throughout the cytoplasm.
• There are sufficient differences between bacterial ribosomes and
eukaryotic ribosomes that some antibiotics will inhibit the functioning of
bacterial ribosomes, but not a eukaryote's, thus killing bacteria but not
the eukaryotic organisms they are infecting.
• Streptomycin binds 70S ribosome and stops protein synthesis but it can
not bind 80S ribosome of eukaryotes and thereby eukaryotic cell remains
unaffected.
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Bacterial Chromosome - Genophore
• The bacterial chromosome consists of a
single,
circle of deoxyribonucleic acid.
• DNA is double stranded- two strands line
up antiparrallel to each other and the bases
are linked together with hydrogen bonds.
• It includes most of the genetic material of
the
organism .
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Bacterial Chromosome
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• Unlike the DNA in eukaryotic cells, which resides
in the nucleus, DNA in bacterial cells is not
sequestered in a membrane-bound organelle
but
appears as a long coil distributed through the
cytoplasm.
• In many bacteria the DNA is present as a single,
circular chromosome and in some cases the
DNA is linear rather than circular.
• some bacteria may contain two chromosomes

Bacterial Chromosome
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• As in all organisms, bacterial DNA contains
the four nitrogenous bases adenine (A),
cytosine (C), guanine (G), and t
• The amount of DNA in bacterial
chromosomes ranges from 580,000 base
pairs in Mycoplasma gallinarum to 4,700,000
base pairs in E. coli to 9,140,000 base pairs in
Myxococcus xanthus.

Inclusion bodies
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• Inclusion bodies: Bacteria can have within their
cytoplasm a variety of small bodies collectively
referred to as inclusion bodies.
• Some are called granules and other are called
vesicles.
• Inclusions are considered to be nonliving
components of the cell that do not possess metabolic
activity and are not bounded by membranes.
• The most common inclusions are glycogen,
lipid droplets, crystals, and pigments.

Inclusion bodies - Granules
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• Granules: Densely compacted substances without a
membrane covering.
• Nutrients and reserves may be stored in the
cytoplasm in the form of glycogen, lipids,
polyphosphate, or in some cases, sulfur or nitrogen
for later use.
• Each granule contains specific substances, such
as glycogen (glucose polymer) and
polyphosphate (phosphate polymer, supplies
energy to metabolic processes).
• Sulfur bacteria contains reserve granules of
sulfur.

Inclusion bodies-vesicles
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• Some aquatic photosynthetic bacteria and cyano
bacteria have rigid gas-filled vacuoles and it helps
in floating at a certain level - allowing them to
move up or down into water layers with different
light intensities and nutrient levels.
• Some magnetotactic bacterium, eg. Aquaspirillium
magnetotacticum , stores Magnetitite (Ferric
oxide). The presence of such magnetic inclusions
enables these bacteria to responds to magnetic
fields.

Microcompartments
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• Microcompartments are widespread,
membrane- bound organelles that are made of a
protein shell that surrounds and encloses
various enzymes.
• Carboxysomes are protein-enclosed bacterial
microcompartments that contain enzymes
involved in carbon fixation.
• Magnetosomes are bacterial
microcompartments, present in magnetotactic
bacteria, that contain magnetic crystals.

Cell Envelope
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• Plasma
Membrane
• Periplasmic Space
• Cell Wall
• Outer membrane

Plasma Membrane
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• Phospholipid bilayer surrounding the cytoplasm
and regulates the flow of substances in and out of
the cell.
• Consists of both lipids and proteins.
• Protects the cell from its surroundings.
• Selectively permeable to ions and organic molecules
and controls the movement of substances in and
out.
• numerous proteins moving within or upon this layer
are primarily responsible for transport of ions,
nutrients and waste across the membrane.

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Periplasmic space
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• Gram-negative bacteria : space between the
cytoplasmic membrane and the cell wall and
space found between cell wall and the outer
membrane
• Periplasm may constitute up to 40% of the total
cell volume in G-ve species.
• Gram-positive bacteria : space between the
cytoplasmic membrane and the cell wall.
• The periplasm is filled with water and proteins
and is reminiscent of the cytoplasm.

Periplasmic Space
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• However periplasm contains proteins and other
molecules distinct from those in the cytoplasm
because the membrane prevents the free
exchange between these two compartments.
• Periplasmic proteins have various functions in
cellular processes including: transport,
degradation, and motility.
• Periplasm controls molecular traffic entering
and leaving the cell.

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Cell wall
• Outer covering of most cells that protects the bacterial cell a
gives it shape (spherical, rod and spiral).
• Composed of peptidoglycan (polysaccharides +
protein)
• Mycoplasma are bacteria that have no cell wall
and therefore have no definite shape.
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Cell wall
• Peptidoglycan - molecule found only in bacterial
cell walls.
• The rigid structure of peptidoglycan gives the
bacterial cell shape, surrounds the plasma membrane
and provides prokaryotes with protection from
the environment
• From the peptidoglycan inwards all bacterial cells
are similar.
• Going further out, the bacterial world divides into
two
major classes: Gram-positive and Gram-negative .
• Amount and location of peptidoglycan in the cell
wall determines whether a bacterium is G+ve or G-
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Peptidoglycan = (polysaccharides +
protein),
• Peptidoglycan (murein) - huge polymer of
interlocking
chains composed of similar monomers.
• peptidoglycan is made from polysaccharide
chains cross-linked by peptides containing D-
amino acids
• The backbone of the peptidoglycan molecule
is composed of two derivatives of glucose:
• N-acetylglucosamine (NAG)
• N-acetlymuramic acid (NAM).
• The NAG and NAM strands are connected by
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Gram-positive Cells
• G+ve bacteria possess thick cell wall containing
many layers of peptidoglycan and teichoic acids.
• In G+ ve cells, peptidoglycan is the outermost structure an
makes up as much as 90% of the thick compact cell wall.
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Gram-negative
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• G-ve bacteria have relatively thin cell wall
consisting of few layers of peptidoglycan
surrounded by a second lipid membrane
containing lipopolysaccharides and lipoproteins
• 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.

Gram Staining
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• Developed in 1884 by Danish scientist Christian
Gram.
• It is a differential stain.
• In this, bacteria are first stained with crystal
violet, then treated with a mordant - a solution
that fixes the stain inside the cell.
• Bacteria are then washed with a decolorizing
agent, such as alcohol, and counterstained with
safranin, a light red dye.

Gram Staining
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• Gram-positive bacteria are those that are
stained
dark blue or violet by Gram staining.
• Gram-negative bacteria cannot retain the
crystal violet stain, instead take up the
counterstain and appearred or pink.
• The walls of gram-positive bacteria have more
peptidoglycans than do gram-negative
bacteria. Thus, gram-positive bacteria retain
the original violet dye and cannot be

Cell wall
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• If the bacterial cell wall is entirely removed, it is
called a protoplast while if it's partially removed,
it is called a spheroplast.
• Antibiotics such as penicillin inhibit the formation
of
peptidoglycan cross-links in the bacterial cell wall.
• The enzyme lysozyme, found in human tears,
also digests the cell wall of bacteria and is the
body's main defense against eye infections.

outer membrane
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• Similar to the plasma membrane, but is less permeable .
• This membrane has tiny holes or openings called porins.
• Porins block the entrance of harmful chemicals and antibiotics,
making G-ve bacteria much more difficult to treat than G+ve cells.
• Composed of lipopolysaccharides (LPS).
• LPS is a harmful substance classified as an endotoxin.
• Lipopolysaccharides, which acts as an endotoxin, are composed of
polysaccharides and lipid A (responsible for much of the toxicity
of G-ve bacteria).
• These differences in structure can produce differences in
antibiotic susceptibility
• Ex: vancomycin can kill only Gram +ve bacteria and is
ineffective against Gram -ve pathogens, such as Haemophilus
influenzae or Pseudomonas aeruginosa.

External structures
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• Flagella
• Pili/fimbriae
• Capsule/slime layer
• Spores(in some bacteria)

Flagella
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• Singular: flagellum
• Long, whip-like semi-rigid cylindrical structures
that aids in cellular locomotion
• Function much like the propeller on a ship.
• about 20 nm in diameter and up to 20 micromts in
length.
• Diameter of a prokaryotic flagellum is about 1/10
th of that of eukaryotic.
• Flagella are driven by the energy released by the
transfer of ions down an electrochemical
gradient across the cell membrane.

Flagella
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• Made up of protein subunits called flagellin.
• Each flagellum is attached to cell membrane
with the help of proteins other than flagellin.
• The basal region has a hook like structure and a
complex basal body. The basal body consists of
a central rod or shaft surrounded by a set of
rings.

Flagella
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• Bacterial spp differ in the number and
arrangement
of flagella on their surface.
• Bacteria may have one, a few, or many flagella
in different positions on the cell.
• Monotrichous - single flagellum
• amphitrichous a flagellum at each end
lophotrichous - clusters of flagella at the poles
of the cell
• peritrichous - flagella distributed over the

Arrangement of flagella
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Flagella
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• Motile bacteria are attracted or repelled by
certain stimuli in behaviors called taxis: these
include chemotaxis, phototaxis, and
magnetotaxis.
• The flagella beat in a propeller-like motion to
help the bacterium move toward nutrients; away
from toxic chemicals; towards the light
(photosynthetic cyanobacteria).
• Prokaryotes exhibit a variety of movements:
move , swim ,tumble ,glide, swarm in response

FIMBRIAE AND PILI
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• Hollow, hair like structures made of protein
• Involved in attachment to solid surfaces or to
other cells and are essential for the virulence of
some bacterial pathogens.
• Fimbriae fine filaments of protein just 2–10 nm
in diameter and up to several micrometers in
length.
• They are distributed over the surface of the
cell, and resemble fine hairs when seen under
the electron microscope.

FIMBRIAE AND PILI
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• Pili: (sing. pilus) are cellular appendages, slightly
larger than fimbriae
• Involved in attachment to surfaces.
• Specialized pili, the sex pili, allows the transfer of
genetic material from one bacteria to another in
a process called conjugation where they are
called conjugation pili or "sex pili".
• type IV pili - generate movement.
• Helps in colonization and pathogenicity.

Glycocalyx
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• Glycocalyx : sticky coating produced by many
bacteria covering the surface of cell.
• The glycocalyx is composed of polysaccharides
(sugars) and proteins.
• The bacterial glycocalyx has 2 forms
 a highly structured rigid capsule
 a disorganised loose slime layer -
• Capsules are found on many pathogenic bacteria

Glycocalyx
• The glycocalyx has several functions including :
protection, attachment to surfaces and
formation of biofilms.
• The glycocalyx helps protect the bacteria cell by
preventing immune cells from attaching to it
and destroying it through phagocytosis.
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Spores
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Bacterial spores are the dormant
forms of bacterial structure which
are thick walled , highly refractile
and resistant.

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ND CULTIVATION/NUTRITION
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Spore
structure :
Spore formation is a means by which
some bacteria haulting their vegetative
phases produces structure that are able
to survive in extremely harsh
environmental conditions.

Shapes
• Spherical , oval or elongated in shape.
• May be narrower or broader(bulge) than parent
cell.
(1) (2)
59

o
Endospore;
 Formed inside the parent vegetative cell.
 Endospores are highly durable dehydrated
cells, which can survive extreme heat, lack of
water, freezing and exposure to many toxic
chemicals and radiation.
 Endospores also called as “resting cells”.
o Exospore ;
 Formed outside the vegetative cell by budding
at one end
of the cell.
 The Exospore do not contain dipicolinic acid.
 They can resist desiccation and
heat.
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Formation :
Exospores are formed external to the
vegetative cell by budding at one end
of the cell . Members of the genus
methylosinus and strains of the
photosynthetic bacterium
rhodomicrobium produce
exospores
These are heat desiccation and UV
Resistant. Is initiated by the appearance
of the bud like enlargement and
surrounding capsule at one end .
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Endospore formation :
When certain essential elements like carbon ,nitrogen and
phosphorus are limited or completely depleted or when water
is unavailable certain gram (+) bacilli from specialized resting
cells called endospores.
These endospores are highly durable dehydrated cells which
can survive extreme heat, lake of water, freezing and exposure
to many toxic chemicals and radiation . The genera of bacteria
giving rise to endospore

 Germination
The germination process
occurs in three stages:
◦Activation
◦Initiation
◦Outgrowth.
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Activation
 Even when placed in an environment
that favors germination (eg.
nutritionally rich medium) bacterial
spores will not germinate unless first
activated by one or another agent that
damages the spore coat.
 Among the agents that can
overcome spore dormancy are heat,
abrasion, acidity, and componds
containing free sulfhydryl groups.
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 Initiation
 Once activated, a spore will initiate germination if
the environmental conditions are favorable.
 Different species have evolved
receptors recognise different effectors as
signaling a rich medium.
 Binding of the effector activates an autolysin that
rapidly degrades the cortex peptidoglycan. Water
is taken up, calcium dipicolinate is released, and a
variety of spore constituents are degraded by
hydrolytic enzymes.
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 Degradation of the cortex and outer
layers
protoplast with its surrounding wall.
 A period of active biosynthesis follows.
This period, which terminates in cell
division, is called outgrowth.
 Outgrowh requires a supply of all
Out
growth
results in the emergence of a new
vegetative cell consisting
of
the spore
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Bacterial reproduction
• Cell growth and reproduction by cell division
are
tightly linked in unicellular organisms.
• Bacteria grow to a fixed size and then
reproduce through binary fission, a form of asexual
reproduction
• Under optimal conditions, bacteria can grow and
divide extremely rapidly, and bacterial populations
can
double as quickly as every 9-8 minutes.
• In cell division, two identical clone daughter cells
are
produced.
• Budding involves a cell forming a protrusion
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Binary fission
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• Most prokaryotes reproduce by a process of binary fission, in
which the cell grows in volume until it divides in half to yield
two identical daughter cells.
• Each daughter cell can continue to grow at the same rate as
its parent.
• For this process to occur, the cell must grow over its entire
surface until the time of cell division, when a new
hemispherical pole forms at the division septum in the middle
of the cell.
• The septum grows inward from the plasma membrane along
the midpoint and forms as the side wall which pinches
inward, dividing the cell in two.
• In order for the cell to divide in half, the peptidoglycan
structure must be different in the hemispherical cap than in the
straight portion of the cell wall, and different wall-cross-linking
enzymes must be active at the septum than elsewhere.

Binary fission
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• Binary fission begins with the single DNA molecule
replicating and both copies attaching to the
cell membrane.
• Next, the cell membrane begins to grow
between the two DNA molecules. Once the
bacterium just about doubles its original size,
the cell membrane begins to pinch inward.
• A cell wall then forms between the two
DNA molecules dividing the original cell into two
identical daughter cells

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Budding
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• A group of environmental bacteria reproduces by budding.
• In this process a small bud forms at one end of the mother
cell
• As growth proceeds, the size of the mother cell
remains about constant, but the bud enlarges.
• When the bud is about the same size as the mother cell, it
separates. This type of reproduction is analogous to that
in budding fungi, such as brewer’s yeast
(Saccharomyces cerevisiae).
• One difference between fission and budding is that, in
the latter, the mother cell often has different properties
from the offspring.
• Ex: In some strains, mother cells have a flagellum and
are motile, whereas the daughter buds lack flagella.

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BACTERIAL
RECOMBINATION
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Three mechanisms of genetic
recombination
• Conjugation
• Transformation
• Transduction
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CONJUGATION
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• Two bacterial cells come together and mate such that a gene transfer
occurs
between them.
• Can only occur between cells of opposite mating types.
– The donor (or "male") carries a fertility factor (F+).
– The recipient ("female") does not (F−).
• One cell, the donor cell (F+), gives up DNA; and another cell, the
recipient cell (F−), receives the DNA.
• The transfer is nonreciprocal, and a special pilus called the sex pilus
joins the donor and recipient during the transfer.
• The channel for transfer is usually a special conjugation tube formed
during
contact between the two cells.
• The DNA most often transferred is a copy of the F factor plasmid.
• The factor moves to the recipient, and when it enters the recipient, it

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BACTERIAL
TRANSFORMATION
• Discovered by Frederick Griffith in 1928.
• Many bacteria can acquire new genes by taking up DNA
molecules (ex: plasmid) from their surroundings.
• When bacteria undergo lysis, they release considerable
amounts of DNA into the environment.
• This DNA may be picked up by a competent cell- one
capable of taking up the DNA and undergoing a
transformation.
• To be competent, bacteria must be in the logarithmic
stage of growth, and a competence factor needed for the
transformation must be present.
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BACTERIAL TRANSDUCTION
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• Bacterial viruses ( bacteriophages) transfer
DNA fragments from one bacterium (the
donor) to another bacterium (the
recipient).
• The viruses involved contain a strand of
DNA
enclosed in an outer coat of protein.

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After a bacteriophage enters a bacterium, it may encourage
the bacterium to make copies of the phage.
 At the conclusion of the process, the host bacterium undergoes
lysis and releases new phages. This cycle is called the lytic
cycle.
Under other circumstances, the virus may attach to the
bacterial chromosome and integrate its DNA into the bacterial
DNA. It may
remain here for a period of time before detaching and continuing
its replicative process. This cycle is known as the lysogenic cycle.
Under these conditions, the virus does not destroy the host
bacterium, but remains in a lysogenic condition with it. The virus
is called a temperate phage, also known as a prophage.
 At a later time, the virus can detach, and the lytic cycle will
ensue.
 It will express not only its genes, but also the genes
acquired from the donor bacterium.
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GROWTH OF
BACTERIA
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Bacterial Growth
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• Growth of Bacteria is the orderly increase
of
all the chemical constituents of the
bacteria.
• Multiplication is the consequence of
growth.
• Death of bacteria is the irreversible loss of
ability to reproduce.

Generation /doubling time
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• Generation time (g) : The time it takes the cells to
double.
• The average generative time is about 20-30
minutes in majority of medically important
bacteria.
• They are some exceptions among pathogenic
bacteria.
• Mycobacterium tuberculosis - 18 hrs.
• Mycobacterium leprae -10-20 days
• Length of generative time is in direct

Growth Kinetics
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• Bacterial growth follows four
phases.
• lag phase
• log phase
• stationary phase
• death phase

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Lag phase
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• Immediately following the seeding of a culture medium.
• A period of adaptation for the cells to their new environment
• cells are adapting to the high-nutrient environment
and preparing for fast growth.
• The lag phase has high biosynthesis rates, as proteins
and metabolic intermediates are built up in adequate
quantities for rapid growth & multiplication to
proceed.
• New enzymes are synthesized.
• A slight increase in cell mass and volume, but no increase in
cell number.

Duration of the lag phase varies
with
- the species
- size of inoculum - Prolonged by low inoculum
volume, poor inoculum condition (high % of dead
cells)
- age of inoculum
- Nature of the culture medium (Prolonged by
nutrient- poor medium)
- And environmental factors like temperature, pH etc
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Log/Exponential growth phase
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• In this phase, the cells have adjusted to their
new environment and multiply rapidly (exponentially)
• The bacteria will grow and divide at a doubling time
characteristic of the strains and determined by the
conditions during the exponential phase.
• During this phase, the number of bacteria will increase to
2n, in which n is the no.of generations.
• Balanced growth –all components of a cell grow at the
same rate.

Deceleration growth phase
Very short phase, during which growth decelerates
due to either:
• Depletion of one or more essential nutrients
• The accumulation of toxic by-products of growth
(e.g. Ethanol in yeast fermentations)
• Period of unbalanced growth: Cells undergo
internal restructuring to increase their chances of
survival
02/02/2025 91

Stationary Phase
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With the exhaustion of nutrients or build-up of toxic
waste substances and secondary metabolic products in
the medium , the bacteria stop growing and enter
the stationary phase.
- The growth rate equals the death rate – The number of progeny
cells
formed is just enough to replace the number of cells that die.
- There is no net growth in the organism population – The viable
count remains stationary as an equilibrium exists between the dying
cells and newly formed cells.

Death Phase
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- Phase of decline
- The living organism population decreases with
time, due to a lack of nutrients and accumulation
of toxic metabolic by-products.
- Cell death may also be caused by autolytic
enzymes.

Generation times
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Bacterium Medium Generation Time (minutes)
Escherichia coli Glucose-salts 17
Bacillus megaterium Sucrose-salts 25
Streptococcus lactis Milk 26
Streptococcus lactis Lactose broth 48
Staphylococcus aureus Heart infusion broth 27-30
Lactobacillus acidophilus Milk 66-87
Rhizobium japonicum Mannitol-salts-yeast extract 344-461
Mycobacterium tuberculosis Synthetic 792-932
Treponema pallidum Rabbit testes 1980

Factors Required for Bacterial
Growth
The requirements for bacterial growth
are:
(A) Environmental factors
(B) Sources of metabolic energy.
02/02/2025 95

Nutrients
02/02/2025 96
• Nutrients in growth media must contain all the
elements necessary for the synthesis of new
organisms.
• Hydrogen donors and acceptors
• Carbon source
• Nitrogen source
• Minerals : sulphur and phosphorus
• Growth factors: amino acids, purines,
pyrimidines;
vitamins

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• Microorganisms are sensitive to temperature changes
– Usually unicellular
– Enzymes have temperature optima
– If temperature is too high, proteins denature,
including enzymes, carriers and structural components
• Temperature ranges are enormous (-20 to 100oC)
Temperature
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Temperature
02/02/2025 99
– Organisms exhibit distinct cardinal
temperatures
(minimal, maximal, and optimal growth temps)
– If an organism has a limited growth
temperature
range = stenothermal (e.g. N. gonorrhoeae)
– If an organism has a wide growth
temperature range = eurythermal (E. faecalis)

Temperature
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Psychrophiles can grow well at 0oC,
have optimal growth at 15oC or lower,
and usually will not grow above 20oC
• Arctic/Antarctic ocean
• Protein synthesis, enzymatic activity and
transport systems have evolved to function
at low temperatures
• Cell walls contain high levels of unsaturated
fatty acids (semi-fluid when cold)

Temperature
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– Psychrotrophs can also grow at 0oC, but have
growth optima between 20oC and 30oC, and growth
maxima at about 35oC
• Many are responsible for food spoilage in refrigerators
– Mesophiles have growth minima of 15 to 20oC, optima
of 20 to 45oC, and maxima of about 45oC or lower
• Majority of human pathogens

Temperature
–Thermophiles have growth minima around
45oC, and optima of 55 to 65oC
• Hot springs, hot water pipes, compost heaps
• Lipids in PM more saturated than mesophiles.
–Hyperthermophiles have growth minima around 55o
and optima of 80 to 110oC
• Sea floor, sulfur vents
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Effect of temperature
02/02/2025 103

Temperature optima of bacteria
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pH
– pH is the negative logarithm of the
hydrogen
ion concentration
– Acidophiles grow best between pH 0 and 5.5
– Neutrophiles grow best between pH 5.5 and 8.0
– Alkalophiles grow best between pH 8.5 and 11.5
– Extreme alkalophiles grow best at pH 10.0 or
higher
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pH
– Sudden pH changes can inactivate
enzymes
and damage plasma membrane
• Reason for buffering culture medium, usually
with a weak acid/conjugate base pair (e.g.
KH2PO4/K2HPO4 – monobasic potassium/dibasic
potassium)
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Bacterial growth at various pH
02/02/2025 107

pH profiles for some prokaryotes
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Organism Minimum pH Optimum pH Maximum pH
Thiobacillus thiooxidans 0.5 2.0-2.8 4.0-6.0
Sulfolobus acidocaldarius 1.0 2.0-3.0 5.0
Bacillus acidocaldarius 2.0 4.0 6.0
Zymomonas lindneri 3.5 5.5-6.0 7.5
Lactobacillus acidophilus 4.0-4.6 5.8-6.6 6.8
Staphylococcus aureus 4.2 7.0-7.5 9.3
Escherichia coli 4.4 6.0-7.0 9.0
Clostridium sporogenes 5.0-5.8 6.0-7.6 8.5-9.0
Erwinia caratovora 5.6 7.1 9.3
Pseudomonas aeruginosa 5.6 6.6-7.0 8.0
Thiobacillus novellus 5.7 7.0 9.0
Streptococcus pneumoniae 6.5 7.8 8.3
Nitrobacter sp 6.6 7.6-8.6 10.0

Oxygen concentration
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– Obligate aerobes are completely dependent
on atmospheric O2 for growth
• Oxygen is used as the terminal electron
acceptor for electron transport in aerobic
respiration
– Facultative anaerobes do not require O2
for growth, but do grow better in its
presence
– Aerotolerant anaerobes ignore O2 and
grow equally well whether it is present or

Oxygen concentration
–Obligate (strict) anaerobes do not tolerate
O2 and die in its presence.
–Microaerophiles are damaged by the normal
atmospheric level of O2 (20%) but require lower leve
to 10%) for growth
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Oxygen and growth
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Environment
Group Aerobic Anaerobic O2 Effect
Obligate Aerobe Growth No growth Required (utilized for
aerobic respiration)
Microaerophile Growth if
level not
too high
No growth Required but at levels
below 0.2 atm
Obligate Anaerobe No growth Growth Toxic
Facultative
(An)aerobe
Growth Growth Not required for growth
but utilized when available
Aerotolerant
Anaerobe
Growth Growth Not required and not
utilized

Anaerobic growth chambers
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Water availability
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• Water is solvent for biomolecules, and its availability
is critical for cellular growth
• The availability of water depends upon its presence
in the atmosphere (relative humidity) or its presence
in solution or a substance (water activity, (Aw))
• Aw of pure water (100%) is 1.0; affected by dissolved
solutes such as salts or sugars.
• Microorganisms live over a range of aW from 1.0 to
0.7. The aW of human blood is 0.99; seawater = 0.98;
maple syrup = 0.90; Great Salt Lake = 0.75. Water
activities in agricultural soils range between 0.9 and
1.0.

Effect of salt on growth
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Pressure
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–
Barotolerant
organisms are
adversely
affected by increased pressure, but not
as
severely as are nontolerant organisms
–Barophilic organisms require, or grow
more rapidly in the presence of
increased pressure
–Light: Optimum condition for growth is
darkness.

Radiation
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-Ultraviolet radiation damages cells by
causing the formation of thymine dimers in
DNA.
– Ionizing radiation such as X rays or gamma
rays are even more harmful to microorganisms
than ultraviolet radiation
• Low levels produce mutations and
may
indirectly result in
death
• High levels are directly lethal by direct
damage
through
the radicals
to cellular macromolecules or
free
production of
oxygen

(B) Sources of Metabolic Energy
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• Mainly three mechanisms generate
metabolic
energy. These are
• Fermentation
• Respiration and
• Photosynthesis.
An organism to grow, at least one of these
mechanisms must be used.

MORPHOLOGICAL
CHARACTERISTICS OF BACTERIA
SIZE- SHAPE-ARRANGEMENT

MORPHOLOGY
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• Bacteria display a wide diversity of shapes and sizes called
morphologies
• Cannot be seen with human eyes (microscopic)
• Their presence was only first recognized in 1677, when the Dutch naturalist Antonie van
Leeuwenhoek saw microscopic organisms in a variety of substances with the aid of
primitive microscopes.
• Now bacteria are usually examined under light microscopes capable of more than
1,000-fold magnification
• Details of their internal structure can be observed only with the
aid of much more powerful transmission electron microscopes.
• Unless special phase-contrast microscopes are used, bacteria have to be stained
with a coloured dye so that they will stand out from their background.

Siz
e
• Bacteria are the smallest living creatures
• Most bacteria are 0.2 um in diameter and 2-8 um in length.
• Bacterial cells are about one tenth the size of eukaryotic cells
• are typically 0.5 – 5.0 micrometres in length.
• Giant bacteria for example, Thiomargarita namibiensis,
Titanospirillum namibiensis and Epulopiscium fishelsoni —
are up to half a mm long and are visible to the unaided eye
• E. fishelsoni reaches 0.7 mm.
• Among the smallest bacteria are members of the genus
Mycoplasma, which measure about 0.1 to 0.25 μm in
diameter, as small as the largest viruses.
• Some bacteria may be even smaller, but these
ultramicro bacteria are not well-studied.
02/02/2025 120

Size
02/02/2025 121
• E. coli, a normal inhabitant of the intestinal tract of
humans and animals, is about 2 μm long and 0.5 μm in
diameter
• spherical cells of Staphylococcus aureus - up to 1 μm
in diameter.
• the rod-shaped Bordetella pertussis, causative agent of
whooping cough - 0.2 to 0.5 μm in diameter and 0.5 to 1
μm in length
• corkscrew-shaped Treponema pallidum, causative agent of
syphilis averaging only 0.15 μm in diameter but 10 to 13
μm in length.
• Some bacteria are relatively large, such as Azotobacter,
which
has diameters of 2 to 5 μm or more
• cyanobacterium Synechococcus averages 6 μm by 12 μm

Cell Shape
• Bacteria come in a wide variety of shapes.
• Coccus – are spherical or oval cells.
• Bacillus - are round-ended cylinder shaped cells.
• Vibrios comma shaped ,curved rods and derive
the
name from their characteristic vibratory motility
• Spirilla – are rigid spiral forms(coil).
• Spirochetes - are long, slender, and flexible spiral
forms(from speira meaning coil and chaite
meaning hair)BACTERIAL STRUCTURE, MORPHOLOGY
02/02/2025 122

Cell Shape
• coccobacilli - Some bacilli are so short and fat
that they look like cocci and are referred to as
coccobacilli.
• A small number of species even have tetrahedral
or cuboidal shapes.
• More recently, bacteria were discovered deep
under the Earth's crust that grow as long rods
with a star-shaped cross-section.
• The large surface area to volume ratio of this
morphology may give these bacteria an
advantage in nutrient-poor environments.
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Cell Shape
• is generally characteristic of a given bacterial species
• but can vary depending on growth conditions.
• Some bacteria have complex life cycles involving the
production of stalks and appendages (e.g.
Caulobacter) and some produce elaborate structures
bearing reproductive spores (e.g. Myxococcus,
Streptomyces).
• Bacteria generally form distinctive cell morphologies
when examined by light microscopy and distinct
colony morphologies when grown on Petri plates.
• These are often the first characteristics observed by a
microbiologist to determine the identity of an
unknown bacterial culture
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Cell Shape
02/02/2025 125
• This wide variety of shapes is determined by
the bacterial cell wall and cytoskeleton
• Shape of the cell is important because it can
influence the ability of bacteria to
acquire nutrients, attach to surfaces, swim
through liquids and escape predators

Arrangement of
cells
• Cellular arrangements occur singularly, in
pairs,
in chains and in clusters.
02/02/2025 126

Bacilli
• Diplobacilli (2 cells), tetrad (4 cells),
palisade (two cells arranged parallel) or
sterptobacilli (chain arrangement)e.g E.Coli
and Salmonella.

Cocci
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Bacilli
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Other shapes
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02/02/2025 132

CULTURAL CHARACTERISTICS OF
BACTERIA
02/02/2025 133

• Culture techniques are designed to promote the
growth and identify particular bacteria,while
restricting the growth of the other bacteria in
the sample.
• In the laboratory, bacteria are usually grown
using solid growth media such as agar plates or
liquid media such as broth.
• Solid, agar-based media can be used to identify
colonial characteristics (shape, size, elevation,
margin type) and to isolate pure cultures of a
bacterial strain
• liquid growth media are used when measurement of
growth or large volumes of cells are required.
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• Growth in stirred liquid media occurs as an even
cell suspension, making the cultures easy to divide
and transfer
• isolating single bacteria from liquid media is
difficult.
• The use of selective media (media with specific
nutrients added or deficient, or with antibiotics
added) can help identify specific org’s.
• Most laboratory techniques for growing bacteria
use high levels of nutrients to produce large
amounts of cells cheaply and quickly.
• However, in natural environments nutrients are
limited, meaning that bacteria cannot continue to
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Cultural characteristics
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Basic conditions for cultivation
• Optimum environmental moisture. It is possible to
cultivate bacteria in liquid media or solid media with
a gelling agent (agar) binding about 90% of water.
• Optimum temperature for cultivation of bacteria of
medical importance is about 370C. Saprophytic
bacteria are able to grow at lower temperatures.
• Optimum pH of culture media is usually 7.2-7.4
Lactobacillus spp need acid pH and vibrio cholera
needs alkaline pH for the growth.
• Optimum constituents of bacteriological culture media.
• All culture media share a number of common
constituents necessary to enable bacteria to grow in
vitro.

Optimum Quantity of oxygen in
cultivation environment.
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• Bacteria obtain energy either by oxidation or by fermentation
i.e.,
oxidation – reduction procedure without oxygen.
• Bacteria are classified into four basic groups according to
their relation to atmospheric oxygen:
• Obligate aerobes: Reproduce only in the presence of
oxygen
• Facultative anaerobes : reproduce in both aerobic and
anaerobic environments. Their complete enzymatic equipment
allows them to live and grow in the presence or absence of
oxygen.
• Obligate anaerobes: grow only in the absence of free oxygen
(i,e unable to grow and reproduce in the presence of oxygen).
Some species are so sensitive that they die if exposed to
oxygen.

Colony morphology
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• Form - the basic shape of the colony
ex: circular, filamentous etc.
• Size – The diameter of the colony.
• Elevation - This describes the side view of a
colony. Turn the Petri dish on end.
• Margin/border - magnified shape of the edge of
the colony
• Surface - colony appearance
ex: smooth, glistening, rough, wrinkled or dull.
• Opacity - ex transparent (clear), opaque,
translucent (like looking through frosted glass), etc.
• Colour (pigmentation) ex: white, buff, red,

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Colony morphology
02/02/2025 140
• Colony morphology is a method that scientists use
to describe the characteristics of an individual
colony of bacteria growing on agar in a Petri dish.
It can be used to help to identify them.
• Each distinct colony represents an individual
bacterial cell or group that has divided
repeatedly. Being kept in one place, the resulting
cells have accumulated to form a visible patch.
• Most bacterial colonies appear white or a
creamy yellow in colour, and are fairly circular in
shape.

Effect of media
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• different types of media, which contain
different nutrients can affect the cultural
characteristics of bacteria.
• Some types of media are much more nutritive and
will encourage hearty growth. Some types of media
may restrict growth.
• Colonial morphology may also be affected by the
temperature at which the bacteria is incubated.
Some bacteria grow better at body temperature and
grow weakly at room temperature, or vice versa.
• Some bacteria express certain characteristics, such
as the formation of pigment, more strongly at some
temperatures than at others.

Cultivation of Bacteria
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BACTERIAL STRUCTURE, MORPHOLOGY AND
CULTIVATION/NUTRITION
142

Cultivation/Culturing of Bacteria
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143
• A microbial culture, is a method of
multiplying microorganisms by letting them
culture
reproduce in predetermined
media under controlled laboratory conditions.
• Microbial cultures are used to determine the
type of organism, its abundance in the sample
being tested, or both.

Purpose of culturing
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144
•
•
Isolation of bacteria.
Properties of bacteria i.e. culturing bacteria is the initial step
in studying its morphology and its identification.
Maintenance of stock
cultures. Estimate viable
counts.
To test for antibiotic
sensitivity.
To create antigens for
laboratory use.
Certain genetic studies and manipulations of the cells
also need that bacteria to be cultured in vitro.
Culturing on solid media is another convenient way
•
•
•
•
•
•

Culture Media
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145
An artificial culture media must provide similar
environmental and nutritional conditions that exist in the
natural habitat of a bacterium.
A culture medium contains water, a source of carbon & energy,
source of nitrogen, trace elements and some growth factors.
The pH of the medium must be set accordingly.
Uses:


Enrich the number of bacteria.
Select for certain bacteria and suppress others.
 Differentiate among different kinds of bacteria.

Pure culture
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• In the laboratory bacteria are isolated and
grown in pure culture in order to study
the functions of a particular specie.
• A pure culture is a population of cells
or growing in the absence of other
species or types. A pure culture may
originate from a single cell or single
organism, in which case the cells are genetic
clones of one another.

• Pure cultures are obtained by using variety of special
techniques. All glassware, media and instruments
must be sterilized i.e. aseptic techniques are used
for obtaining pure cultures.
Basic requirement for obtaining a pure culture
are solid medium, a media container that can
be maintained in an aseptic condition and a
method to separate individual cell.
A single bacterium, supplied with right nutrients, will
multiply on the solid medium in a limited area
to form a colony, which is a mass of cells all
descended from the original one.
•
•
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Agar
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148
• Agar, a polysaccharide extracted from marine algae,
is used to solidify a specific nutrient solution.
Unlike other gelling agent, it is not easily degraded
by many bacteria.
It is not easily destroyed at higher temperatures, and
therefore it can be sterilized by heating, the process
which also liquefies it.
Once solidified, agar medium will remain solid until
•
•
•
✓ The culture media is contained in a Petri dish, a two
part, glass or plastic covered container.

Classification of Culture Media
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• Bacterial culture media can be classified in
at least three ways.
1. Consistency
2. Nutritional component
3. Functional use

Classification based on consistency
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1. Liquid media.
2. Solid media.
3. Semi solid
media.

Classification based on consistency:
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151
A. Liquid media: These are available for use in test-tubes, bottles or flasks.
Liquid media are sometimes referred as “broths” (e.g nutrient broth). In
liquid medium, bacteria grow uniformly producing general turbidity. No
agar is added. Mostly used for inoculums preparation.
B. Solid media: An agar plate is a Petri dish that contains a growth medium
(typically agar plus nutrients) used to culture microorganisms. 2%
of agar is added. Agar is the most commonly used solidifying agent.
Colony morphology, pigmentation, hemolysis can be appreciated.
Examples include Nutrient agar and Blood agar.
C. Semi-solid media: Such media are fairly soft and are useful in
demonstrating bacterial motility and separating motile from non-motile
strains. Examples of Semi-solid
media fermentation). 0.5% agar is
added.
(Hugh & Leifson’s oxidation

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153

Classification based on Nutritional
Components
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154
1. Simple media.
2. Complex media.
3. Synthetic or chemically defined
media.

Classification based on Nutritional
Components
1. Simple media: Simple media such as peptone water, nutrient agar can
support most non-fastidious bacteria. It is also called as basal media.
Eg: NB, NA. Nutrient Broth consists of peptone, yeast extract and
NaCl. When 2% of agar is added to Nutrient Broth it forms Nutrient
agar.
2. Complex media. Media other than basal media are called
complex media. They have special ingredients in them for the
growth of microorganisms. These special ingredients like yeast
extracts or casein hydrolysate, which consists of a mixture of
many chemicals in an unknown proportion.
3. Synthetic media/Chemically defined media: Specially prepared
media for research purposes where the composition of every
component is well known. It is prepared from pure chemical
substances. Eg: peptone water (1% peptone + 0.5% NaCl in water).
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Classification based on Functional Use or
Application
1. Enriched media.
2. Selective media.
3. Differential media.
4. Transport media.
5. Indicator media.
6. Anaerobic media.
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Classification based on Functional Use or Application
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157
1. Enriched
media :
• Addition of extra nutrients in the form blood, serum, egg
yolk etc to basal medium makes them enriched media.
Media used to isolate pathogens from a mixed culture.
Stimulate growth of desired bacterium and inhibit growth
of unwanted bacterium
Media is incorporated with inhibitory substances to
suppress the unwanted organism, thus increase in numbers
of desired bacteria.
•
•
•
Examples of Enriched media: Chocolate agar Blood
agar.
•
•
•
Selenite F Broth – for the isolation of Salmonella,
Shigella. Tetrathionate Broth – inhibit coliforms .
Alkaline Peptone Water – for Vibrio cholerae.

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• Chocolate Agar • Chocolate agar - is a non-selective,
enriched growth medium used for growing fastidious
bacteria, such as Haemophilus influenzae .
• Blood Agar • Blood agar plate (BAP)
Contains mammalian blood (usually sheep or
horse), typically at a concentration of 5– 10%.
BAP are enriched, differential media used to
isolate fastidious organisms and detect hemolytic
activity.
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160

2. Selective
media:
• The inhibitory substance is added to a solid
media thus causing an increase in number of
colonies of desired bacterium.
• Selective media and enrichment media are designed
to inhibit unwanted commensal or contaminating
bacteria and help to recover pathogen from
a mixture of bacteria.
Any agar media can be made selective by addition
of certain inhibitory agents that don’t affect
the pathogen. To make a medium selective
include addition of antibiotics, dyes, chemicals,
alteration of pH or a combination of these.
•
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Examples of Selective media :
• Thayer Martin Medium selective for Neisseria gonorrhoeae.
• EMB agar is selective for gram-negative bacteria. The
dye methylene blue in the medium inhibits the growth of
gram- positive bacteria; small amounts of this dye effectively
inhibit the growth of most gram-positive bacteria.
• Campylobacter Agar
(CAMPY) isolation of
Campylobacter jejuni.
is
used
for the selective
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EMB agar Campylobacter
agar
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163

3. Differential Media
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164
• Certain media are designed in such a way that different
bacteria can be recognized on the basis of their colony color.
Various approaches include incorporation of dyes, metabolic
substrates etc, so that those bacteria that utilize them appear
as differently colored colonies. Substances incorporated in it
enable it to distinguish between bacteria.
Example of differential media:MacConkey’s agar,
CLED agar, XLD agar etc.
• XYLOSE LYSINE DEOXYCHOLATE AGAR • XLD is used as a
selective and differential medium for the recovery
of Salmonella and Shigella species.

• CYSTEINE LACTOSE ELECTROLYTE DIFFECIENT AGAR • C.L.E.D.
Agar is a non selective solid medium for cultivation of
pathogens from urine specimens. Lack of salts (electrolytes)
inhibits swarming of Proteus spp.
• MacConkey Agar culture medium designed to grow Gram-
negative bacteria and differentiate them for lactose
fermentation. It contains bile salts (to inhibit most
Gram- positive bacteria), crystal violet dye (which also
inhibits certain Gram-positive bacteria). Lactose
fermenters – Pink colonies and Non lactose fermenters –
colourless colonies.
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Mac’Conkey Agar C.L.E.D Agar
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166

Growth of pathogenic E.coli on CLED
agar
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4. Transport Media
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168
• Clinical specimens must be transported to the laboratory
immediately after collection to prevent overgrowth of contaminating
organisms or commensals. Delicate organisms may not survive the
time taken for
transporting the specimen without a
transport achieved by using transport media.
Transport media should fulfill the following criteria:
media. This can be
• Temporary storage of specimens being transported to the laboratory for
cultivation.
Maintain the viability of all organisms in the specimen without
altering their concentration.
Contain only buffers and salt.
Lack of carbon, nitrogen, and organic growth factors so as to
prevent microbial multiplication.
Transport media used in the isolation of anaerobes must be free
of molecular oxygen.
•
•
•
•

Example of Transport
media:
•
•
•
Cary Blair medium for campylobacter species.
Alkaline peptone water medium for vibrio cholerae.
Stuart’s medium – non nutrient soft agar gel
containing a reducing agent & charcoal used for
Gonnococci.
Buffered glycerol saline for enteric bacilli.
•
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170

5. Indicator Media
•Eg: Wilson-Blair medium – S. typhi forms black colonies.
•McLeod’s medium (Potassium tellurite)– Diphtheria bacilli.
•Urease media: Urea → CO2 + NH3.
•NH3 → Medium turns pink
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• Contains an indicator which changes its color when
a bacterium grows in them.
•
•
•

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173

6. Anaerobic media
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174
• Anaerobic bacteria need special media for
growth because they need low oxygen content,
reduced oxidation –reduction potential and extra
nutrients.
Media for anaerobes may have to be supplemented
with nutrients like hemin and vitamin K.
Boiling the medium serves to expel any
dissolved oxygen.
•
•
Example of Anaerobic media:
• Thioglycollate medium.

Thioglycollate medium
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Culture Methods
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176

Culture Methods
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177
•
•
•
•
•
Streak culture
Lawn culture
Stroke
culture Stab
culture
Pour plate
method

Streak culture
Used for the isolation of bacteria in pure culture from
clinical specimens.
• Platinum wire is used.
• One loop full of the specimen is transferred onto the surface
of a well dried plate.
• Spread over a small area at the periphery.
• The inoculum is then distributed thinly over the plate by
streaking it with a loop in a series of parallel lines in different
segments of the plate.
• On incubation, separated colonies are obtained over the last
series of streaks.
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Lawn Culture
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181
• Provides a uniform surface growth of the bacterium.
•Lawn cultures are prepared by flooding the surface
of the plate with a liquid suspension of the
bacterium
• Uses
– For bacteriophage typing.
– Antibiotic sensitivity testing.
– In the preparation of bacterial antigens and vaccines.

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Stroke Culture
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• Stroke culture is
made in tubes
containing agar slope /
slant.
Uses:
Provides a pure growth
of bacterium for slide
agglutination and
other diagnostic tests.

Stab Culture
• Prepared by puncturing a suitable medium – gelatin or glucose agar with a
straight, charged wire.
•Uses
– Demonstration of gelatin liquefaction.
– Oxygen requirements of the bacterium under study.
– Maintenance of stock cultures.
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Pour Plate Culture
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• 1 ml of the innoculum is added to the molten
agar.
• Mix well and pour to a sterile Petri dish.
• Allow it to set.
•
depth of the medium.
Uses:
– Gives an estimate
of the viable suspension.
– For the quantitative urine cultures.
bacterial count in a

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MPS 206 Bacteriology Lecture 3 and 4 Notes.pptx

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MPS 206 Bacteriology Lecture 3 and 4 Notes.pptx