Bacteria

Bacteria
-
General Microbiology
This set of lecture is strictly for personal use

and may not be copied, reproduced, used, or
distributed in any way. 1
Lecturer: Esra Dandin

Prokaryotes
 Can be found almost everywhere
 They are adaptable to extreme conditions
 They are metabolically flexible/adaptable
 5x10^30 bacteria on earth
 Prokaryotes, especially bacteria, outnumber human cells 10:1

in human body
 (microbiome - human mouth, nasal cavity, throat, ears,

gastrointestinal tract, skin, vagina)
2
 Lack of membraned-nuclei (Instead, genetic
material in nucleoid and plasmid)
 Lack of membrane-bound organelles such as

mitochondria, chloroplast, E.R. etc.
3
Morphology of Bacteria
 Spherical (coccus), rod-shaped (bacillus), curved
(spirillum, spirochete, or vibrio)
 They may have flagella, pili, capsule external to

the cell wall.
4
 Cell division pattern: Biniary fission
 Identification methods for bacteria:

 Biochemical tests
 DNA/RNA analysis
 Serological testing methods
5
Bacterial Cell Structure: Cell Wall
 Composition of cell wall is unique for bacteria
 Exceptions: Mycoplasma and archeabacteria do not

have cell walls
 Cell wall structure also determines whether the

bacteria is gram positive or negative (See later)
 Pores (Gram positive) and porins (channel-like

structures in gram negative) in cell wall allowing
diffusion of metabolites
6
 Main constituent of cell wall: Murein ( a.k.a. Peptidoglycan)
 Peptidoglycan layer (Murein):

 Provides a rigid texture to cell wall
 Made of carbohydrate and aminoacids
 Surrounds cytoplasmic membrane
 Determines the shape of the cell
Gram negative cell wall Gram positive cell wall

7
Note
 Lysozyme enzyme provides immunological defence
against bacterial infections.
 Peptidoglycan (found in cell wall of bacteria) is the

substrate target of lysozyme.
 Lysozyme breaks down peptidoglycan and whole cell

get disrupted.
 Also, murein is a target for antibiotics.

8
Gram Positive Bacteria
 Identified by Gram
Staining technique
 Thick, single layer of

peptidoglycan (Murein)
 Teichoic acid is important

for pathogenesis.
9
 Teichoid acid in cell wall promotes adherence
to host tissues
 It is a specific surface antigen for bacteria
 Antibodies produced against one type of

bacterial surface antigen is not effective on the
other surface antigen
 M protein in the cell wall of Streptococcus

Pyogenes enhances pathogenesis by protecting
bacteria against phagocytosis
10
Gram Negative Bacteria
 One more layer

external to the
murein
 Outer membrane is
unique for bacteria.
It protects gram
negative bacteria
against lysozyme.
11
 Murein is thin and
contains phospholipid
 Outer layer is thicker

and contains
lipopolysaccharides
 Periplasmic space is a
site for enzyme
function
 Composition of outer
layer provides
endotoxin function to
the bacteria 12
 Lipid A part of
lipopolysaccharides
function as endotoxin.
 When bacterial cell is

broken down in
human body, lipid A is
released causing
fever, diarrhea,
shock…
13
Example:
 E. coli O157:H7 causes severe infections
 It is transmitted from contaminated
hamburger meat
14
Gram Posivite vs. Gram Negative
Plasma membrane + cell wall = Cell envelope

15
Cytoplasmic Membrane
 Encloses cytoplasm
 Phospholipid bilayer (20-30%) + protein (50-70%)
 No sterol included in cell membrane

 Differs from eukaryotic cell membrane
 Semi-permable, flexible
 Specific receptors for active transport of large

substances (apart from water) 16
Cell membrane of bacteria is a place for:
 Cellular respiration
 Photosynthesis
 Synthesis of lipids and cell wall components
 Replication
 Contains special receptor molecules for response

to the chemicals in the environment
(Chemotaxis)
17
Cytoplasmic Matrix
 No membrane-bound organelles
 Contains:
 Organic and inorganic substances
 Ribosomes
 Genetic material
 Inclusion granulles
 Water
18
Capsule
 Glycocalyx layer surrounding
bacterial cell in some bacteria
 It is called as ‘capsule’ when

glycocalyx layer is strongly
adherent to cell wall and its
shape is well defined
 If it hold on to cell wall loosely

and its shape is not precise, then
it is called as ‘slime’ layer 19
 Capsule is not necessary for growth
 It protects bacteria from phagocytosis so that

increases its virulence (pathogenesis)
 Slime layer enables bacteria to form microcolonies by

adhering to each other and to the surface. This
microcolonies (bacteria gruops) are so big for
phagocyte to engulf.
20
Flagella
 Singular form: Flagellum
 Originated from cytoplasm
 External to cell wall
 Made of protein subunits called flagellin
 Main function: Bacterial movement
 Movement by flagella is usually directed as a response to attractants in

the environment
Bacteria reaches to nutrients and move away from poisons by

flagella (Chemotaxis) 21
(1) Polar, monotrichous
(2) Lophotrichous
(3) Bipolar, monotrichous
(4) Peritrichous
22
Interesting Fact!
Bacteria can move 3000 times of its length away

per minute whereas a cheetah can move 1500
times of its length away per minute
23
Fimbriae = Pili
 Main function: Adherence to the surfaces (of host e.g.)
 Made of protein subunits called ‘pilin’
 Shorter and thinner than flagella and distributed over

the bacterial surface
 Only seen under electron microscope
 Most gram negative bacteria have pili; few gram

positives do.
 If no fimbria, then bacteria uses surface proteins to adhere to
targets. 24
Sex Pilus
 Sex Pili: Tube for chromosome transfer from
bacteria to bacteria
 This process is known as conjugation
 1-4 sex pili per bacterial cell
25
Spore
 Bacillus and Clostridium bacteria can form spores
 Spores does not function to reproduce whereas they are

important for survival of bacteria
 Bacteria has vegetative and dormant (spore) state
 Bacteria can maintain its all functions in vegetative state

under normal conditions
 Whereas spore state is necessary for survival in extremely

harsh conditions for bacteria
26
 Lower water content in spore form (5-10%)
meaning a protection against high temperature
 Decreased metabolical activity
 Calcium content in spore contributes to

protection
 No specific antigen of spore identified
27
 Spore protects bacteria from harmful
conditions such as extreme heat,
ultraviolet, chemicals…
 Bacteria can turn into spore state in 6-8

hours
 Whereas it can turn into vegetative stage

in 90 minutes
 Cell membrane curls up internally to

cytoplasm takes up choromosome,
ribosome and other materials needed and
eventually endospore is formed. 28
Inclusion Bodies
 Granules of organic and inorganic material used

for storage for metabolic actions
 In form of Lipid, glycogen, calcium, sulfur,

polyphosphate etc.
29
Genome of Bacteria
 Nucleiod: Consisted of
one circular chromosome
and double-stranded
DNA
 Approximately 2000-
3000 genes
 Plasmids (dispensable)
30
Plasmid
 Found in many bacteria
 Circular DNA molecules in cytoplasm
 They exist in bacteria as an extra to chromosome
 Not necessarily dependent to chromosome (e.g. Self-

replicated)
 Provides resistance to antibiotics and disinfection
31

32
Stages of Infection
1. Transmission: Bacterial entry to human body
2. Adhesion: Reaching targeted place in host and

holding on to there
3. Invasion: Reproduction in area
4. Tissue damage
33
Virulence = Strenght of Pathogenicity
 The number of bacteria
 Replication rate
 Adhesions (Colonization)
 Invasion factors
 Endotoxins and exotoxins
 The ability to avoid the immune system 34

Exotoxins:
 Secreted by living bacteria to the environment
 Mostly by Gram positive bacteria
 Very toxic
 Cause bacterial toxin-specific clinical consequences in

host
 Inactivated toxins can be used as vaccines
 Examples: Cholera toxin, botulinum toxin, diphtheria

toxin, tetanus toxin
35
Endotoxins:
 Found in Gram negative bacteria cell wall
 Released when bacterial cell is broken down
 Less toxic compared to exotoxins
 No bacterial toxin-specific clinical consequences
 Initiates inflammatory response in host: Fever,

shock…
36
Learning Outcomes
You should be able to:
 Explain functions of cell membrane, flagella,
fimbria, spore, capsule
 Explain characteristics of bacterial cell wall
 Describe virulence factors
 Describe bacterial gene transfer

37
Thanks!
38

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This set of lecture is strictly for personal use

Lecturer: Esra Dandin

 They are adaptable to extreme conditions

 They are metabolically flexible/adaptable

 5x10^30 bacteria on earth

 Prokaryotes, especially bacteria, outnumber human cells 10:1

 (microbiome - human mouth, nasal cavity, throat, ears,

 Lack of membrane-bound organelles such as

 They may have flagella, pili, capsule external to

 Identification methods for bacteria:

 Exceptions: Mycoplasma and archeabacteria do not

 Cell wall structure also determines whether the

 Pores (Gram positive) and porins (channel-like

 Peptidoglycan layer (Murein):

Gram negative cell wall Gram positive cell wall

 Peptidoglycan (found in cell wall of bacteria) is the

 Lysozyme breaks down peptidoglycan and whole cell

 Also, murein is a target for antibiotics.

 Thick, single layer of

 Teichoic acid is important

 It is a specific surface antigen for bacteria

 Antibodies produced against one type of

 M protein in the cell wall of Streptococcus

 One more layer

 Outer layer is thicker

 When bacterial cell is

Plasma membrane + cell wall = Cell envelope

 Phospholipid bilayer (20-30%) + protein (50-70%)

 No sterol included in cell membrane

 Specific receptors for active transport of large

 Contains special receptor molecules for response

 It is called as ‘capsule’ when

 If it hold on to cell wall loosely

 It protects bacteria from phagocytosis so that

 Slime layer enables bacteria to form microcolonies by

 Originated from cytoplasm

 External to cell wall

 Made of protein subunits called flagellin

 Main function: Bacterial movement

 Movement by flagella is usually directed as a response to attractants in

Bacteria reaches to nutrients and move away from poisons by

(3) Bipolar, monotrichous

Bacteria can move 3000 times of its length away

 Made of protein subunits called ‘pilin’

 Shorter and thinner than flagella and distributed over

 Only seen under electron microscope

 Most gram negative bacteria have pili; few gram

 Spores does not function to reproduce whereas they are

 Bacteria has vegetative and dormant (spore) state

 Bacteria can maintain its all functions in vegetative state

 Whereas spore state is necessary for survival in extremely

 Decreased metabolical activity

 Calcium content in spore contributes to

 No specific antigen of spore identified

 Bacteria can turn into spore state in 6-8

 Whereas it can turn into vegetative stage

 Cell membrane curls up internally to