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Bacteria –
Morphology &Classification
Dr. Ashish Jawarkar Consultant Pathologist
Parul Sevashram Hospital
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Learning Objectives
After completing this section you should be able toperform the following objectives:
list the differences between prokaryotic and eukaryotic cell
Describe the structure of a bacterial cell and explain the
function of its components
Explain why cell wall forms the basis for classification of
bacteria
Explain the structural modifications (flagella) of the cell and
their functional importance
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Size of Bacteria
Unit of measurement in bacteriology is themicron (micrometre, µm)
1 micrometre (10-6)= 1/1000 mm =
1/10000 cm = 1/100000 metre1 nanometer (10-9)= 1/1000 micrometer =
1/100000000 meter
Bacteria of medical importance0.2 – 1.5 µm in diameter
3 – 5 µm in length
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Prokaryotic Cells
prokaryotes are molecules surrounded by amembrane and cell wall.
they lack a true nucleus and don’t have
membrane bound organelles like mitochondria,etc.
large surface-to-volume ratio : nutrients caneasily and rapidly reach any part of the cellsinterior
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Anatomy of a Bacterial Cell
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Structure & Function of Cell
Components
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CELL WALL
Outermost layer, encloses cytoplasm
1.Confers shape and rigidity
2.10 - 25 nm thick
3.Composed of peptidoglycan
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Cell Wall
Cell wall – 4.Chemical nature of the cell wall helps to divide
bacteria into two broad groups – Gram positive &
Gram negative
5.Carries bacterial antigens – important in virulence &immunity – gm –ve cell wall has lipopolysachhrides –
fever and necrosis
6.Several antibiotics may interfere with cell wall
synthesis e.g. Penicillin, Cephalosporins
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Gram positive cell wall
The Gram-positive cell wall is composed of a thick, multilayered
peptidoglycan sheath outside of the cytoplasmic membrane. Teichoic
acids are linked to and embedded in the peptidoglycan, and lipoteichoic
acids extend into the cytoplasmic membrane
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Gram negative cell wall
The Gram-negative cell wall is composed of an outer membrane linked tothin, mainly single-layered peptidoglycan by lipoproteins.The outer
membrane includes porins, which allow the passage of small hydrophilic
molecules across the membrane, and lipopolysaccharide molecules that
extend into extracellular space.
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Cytoplasmic (Plasma) membrane
Thin layer 5-10 nm, separates cell wall fromcytoplasm
Acts as a semipermeable membrane: controlsthe inflow and outflow of metabolites
Composed of lipoproteins with small amounts of
carbohydrates
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Other Cytoplasmic Components
Ribosomes – protein synthesis
Mesosomes – 1.Multilaminated structures formed as
invaginations of plasma membrane2.Principal sites of respiratory enzymes
Intracytoplasmic inclusions – reserve of energy
& phosphate for cell metabolism e.g.Metachromatic granules in diphtheria bacilli
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Nucleus
No nucleolus
No nuclear membraneGenome –
single, circular double stranded DNA.
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Additional Organelles
1. Plasmid – Extranuclear genetic elements consisting of
DNA
Transmitted to daughter cells
Confer certain properties e.g. drug
resistance, toxicity
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Additional Organelles2. Capsule –
Viscous layer secreted around the cellwall.
Polysaccharide / polypeptide in nature
Capsule – sharply defined structure,antigenic in nature
• Protects bacteria
• Stained by negative staining using IndiaInk
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Additional Organelles3. Flagella –
Long (3 to 12 µm), filamentous surface appendages
Organs of locomotion
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Types of flagellar arrangementPolar/ Monotrichous – single
flagellum at one pole
Lophotrichous – tuft of flagella at one
pole
Peritrichous – flagella all over
Amphitrichous – flagella at both
poles
Amphilophotrichous – tuft of flagella
at both ends
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Additional Organelles4. Fimbriae/ Pili –
Thin, hairlike appendages on the surface of many Gram-negative bacteria
10-20µ long, acts as organs of adhesion
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Additional Organelles5. Spores –
Highly resistant restingstages formed during adverseenvironment (depletion of nutrients)
Formed inside the parent cell,hence called Endospores
Very resistant to heat,radiation and drying and can
remain dormant for hundredsof years.
Formed by bacteria likeClostridia, bacillus
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Differences between prokaryotic & eukaryotic cells
Character Prokaryotes Eukaryotes
Nucleus Nuclear membrane
Absent Present
Nucleolus Absent Present
Chromosome One circular One or more
paired and linear
Cytoplasmi
c
membrane
Structure and
Composition
fluid phospholipid
bilayer, lacks
sterols
fluid phospholipid
bilayer containing
sterols
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Differences between prokaryotic & eukaryotic cells
Character Prokaryotes EukaryotesCytoplasm Mitochondria Absent Present
Lysosomes Absent Present
Golgiapparatus
Absent Present
Endoplasmic
reticulum
Absent Present
Vacuoles Absent Present
Ribosomes Present Present
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Differences between prokaryotic & eukaryotic cells
Character Prokaryotes Eukaryotes
Cell Wall Present Absent
Except Fungi
Locomotor
organelles
Flagella Flagella/ Cilia
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Binary Fission
DNA replication
Plasma membrane invaginate
Cell wall deposited in invaginated space
Cross wall completed
Cells separate
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Binary Fission
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Bacterial Growth Curve
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Bacterial Growth Curve
1 5 10
Time (hours)
Lag phase
Log phase
Stationary phase
Death
phase
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G: Generation time
Time in minutes or hours for a
population of bacteria to double in
number
Calculation of Generation Time
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Calculation of Generation Time
1 5 10
Time (hours)
Log phase
Double
# cells
Generation time
Log Number of Bacteria
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Minimum Growth requirements
Water as a source of carbon
Nitrogen source
Inorganic salts like phosphate, sulphate,sodium, potassium, iron etc – need to be
supplied in culture media
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Phototrophs – derive energy from sunlight
Chemotrophs – from chemical reactions
Autotrophs –
synthesize organiccompounds
Heteretrophs – cannot synthesize, depend
on others
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Oxygen requirement
Aerobic – V. cholera
Anaerobic - Clostridia
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Carbon dioxide
All require
Some like Brucella, req 5-10% k/a
capnophilic
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Temperature
Mesophilic – 25-40
Psychrophilc - <20
Thermophilic –
55-80Except thermophilic, most die at 50-60, k/a
thermal death point
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Other factors
Moisture
pH