This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

1. Bacteria – Morphology &
Classification
Dr. Ashish Jawarkar
Consultant Pathologist
Parul Sevashram Hospital

2. Learning Objectives

After completing this section you should be able to
perform 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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3. Size of Bacteria
 Unit
of measurement in bacteriology is the
micron (micrometre, µm)
 1 micrometre (10-6)= 1/1000 mm = 1/10000
cm = 1/100000 metre
 1 nanometer (10-9)= 1/1000 micrometer =
1/100000000 meter
 Bacteria of medical importance
 0.2
– 1.5 µm in diameter
 3 – 5 µm in length
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6. Introduction:
 Based
on the organization of their cellular
structures, all living cells can be divided into two
groups: eukaryotic and prokaryotic

Eukaryotic cell types - Animals, plants, fungi,
protozoans

Prokaryotic cell types - bacteria
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7. Prokaryotic Cells
 prokaryotes
are molecules surrounded by a
membrane and cell wall.
 they
lack a true nucleus and don’t have
membrane bound organelles like mitochondria,
etc.
 large
surface-to-volume ratio : nutrients can
easily and rapidly reach any part of the cells
interior
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8. Anatomy of a Bacterial Cell
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9. Anatomy of A Bacterial Cell

Outer layer – two components:
1.
2.
Rigid cell wall
Cytoplasmic (Cell/ Plasma) membrane – present
beneath cell wall

Cytoplasm – cytoplasmic inclusions,
ribosomes, mesosomes, genetic material

Additional structures –capsule, flagella,
fimbriae (pili), spores
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10. Structure & Function of Cell
Components

11. CELL WALL

Outermost layer, encloses cytoplasm
1. Confers
2. 10
shape and rigidity
- 25 nm thick
3. Composed
of peptidoglycan
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12. 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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13. 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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14. Gram negative cell wall
The Gram-negative cell wall is composed of an outer membrane linked to
thin, 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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15. Cytoplasmic (Plasma) membrane

Thin layer 5-10 nm, separates cell wall from
cytoplasm

Acts as a semipermeable membrane: controls
the inflow and outflow of metabolites

Composed of lipoproteins with small amounts of
carbohydrates
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17. Other Cytoplasmic Components

Ribosomes – protein synthesis

Mesosomes –
Multilaminated structures formed as
invaginations of plasma membrane
2. Principal sites of respiratory enzymes
1.

Intracytoplasmic inclusions – reserve of energy
& phosphate for cell metabolism e.g.
Metachromatic granules in diphtheria bacilli
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19. Nucleus
 No
nucleolus
 No nuclear membrane
 Genome –
 single,
circular double stranded DNA.
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20. 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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21. Additional Organelles
2.
Capsule–



Viscous layer secreted around the cell
wall.
Polysaccharide / polypeptide in nature
Capsule – sharply defined structure,
antigenic in nature
•
•
Protects bacteria
Stained by negative staining using India
Ink
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22. Additional Organelles
3.
Flagella –

Long (3 to 12 µm), filamentous surface appendages

Organs of locomotion
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23. Types of flagellar arrangement
Polar/ Monotrichous – single
flagellum at one pole
Lophotrichous – tuft of flagella at
one pole
Amphitrichous – flagella at both
poles
Peritrichous – flagella all over
Amphilophotrichous – tuft of flagella
at both ends
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24. Additional Organelles
4.
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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25. Additional Organelles
5.
Spores –

Highly resistant resting
stages formed during adverse
environment (depletion of
nutrients)

Formed inside the parent cell,
hence called Endospores

Very resistant to heat,
radiation and drying and can
remain dormant for hundreds
of years.

Formed by bacteria like
Clostridia, bacillus
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26. Differences between prokaryotic & eukaryotic cells
Character
Eukaryotes
Nuclear
membrane
Absent
Present
Nucleolus
Absent
Present
Chromosome
Nucleus
Prokaryotes
One circular
One or more
paired and linear
fluid phospholipid
bilayer, lacks
sterols
fluid phospholipid
bilayer containing
sterols
Cytoplasmi Structure and
c
Composition
membrane

27. Differences between prokaryotic & eukaryotic cells
Character
Cytoplasm
Prokaryotes
Eukaryotes
Mitochondria
Absent
Present
Lysosomes
Absent
Present
Golgi
apparatus
Absent
Present
Endoplasmic
reticulum
Absent
Present
Vacuoles
Absent
Present
Ribosomes
Present
Present
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28. Differences between prokaryotic & eukaryotic cells
Character
Prokaryotes
Eukaryotes
Cell Wall
Present
Absent
Except Fungi
Locomotor
organelles
Flagella
Flagella/ Cilia
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30. GROWTH AND MULTIPLICATION
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31. Binary Fission
 DNA
replication
 Plasma membrane invaginate
 Cell wall deposited in invaginated space
 Cross wall completed
 Cells separate
07.09.08
Dr. Ashish Jawarkar

32. Binary Fission
 Light
07.09.08
micrograph
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33. Binary Fission
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34. Consequences of Binary Fission
 Very
large number of cells very fast
 Mathematical progressions
 arithmetic
(1>2>4>6>8>10>12>14>16)
 geometric(1>2>4>8>16)
 exponential
expression (20 > 21 > 22 >23>24)
 logarithmic expression(0 >log 1>log 2>log 3>log 4)
2
2
2
2
07.09.08
Dr. Ashish Jawarkar

35. Bacterial Growth Curve
Stationary phase
Death
phase
Log phase
Lag phase
1
07.09.08
5
Time (hours)
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36. G: Generation time
Time in minutes or hours for a
population of bacteria to double in
number

37. Calculation of Generation Time
Log Number
of Bacteria
Double
# cells
Log phase
Generation time
1
07.09.08
5
Time (hours)
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38. GENERATION TIME / population
doubling time
 E-coli
– 20 min
 MTb - 20 hours
 Mleprae - 20 days
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39. 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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40.  Phototrophs
– derive energy from sunlight
 Chemotrophs – from chemical reactions
 Autotrophs – synthesize organic
compounds
 Heteretrophs – cannot synthesize, depend
on others
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41. Oxygen requirement
 Aerobic
– V. cholera
 Anaerobic - Clostridia
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42. Carbon dioxide
 All
require
 Some like Brucella, req 5-10% k/a
capnophilic
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43. Temperature
 Mesophilic
– 25-40
 Psychrophilc - <20
 Thermophilic – 55-80
 Except thermophilic, most die at 50-60, k/a
thermal death point
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44. Other factors
 Moisture
 pH
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