Transcript of Assist. Prof. Emrah Ruh NEU Faculty of Medicine Department of Medical Microbiology Bacterial Cell...
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- Assist. Prof. Emrah Ruh NEU Faculty of Medicine Department of
Medical Microbiology Bacterial Cell Structure
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- Bacterial cell structure Cytoplasmic structures Nucleoid
Ribosome Cytoplasmic membrane Cell wall External structures
Cytoplasmic structures Nucleoid Ribosome Cytoplasmic membrane Cell
wall External structures
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- Bacterial cell structure Nucleoid Prokaryotes: No true nucleus;
no nuclear membrane, no nucleolus Bacterial chromosome: Single,
double- stranded circle found in the nucleoid
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- Bacterial cell structure Ribosome Prokaryotic cell: 70S
ribosome (30S + 50S subunits) Eukaryotic cell: 80S ribosome (40S +
60S subunits)
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- Bacterial cell structure Cell membrane Lipid bilayer structure
Does not usually contain sterols
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- Bacterial cell structure Cell membrane Functions Selective
permeability and transport of solutes Electron transport and
oxidative phosphorylation Excretion of hydrolytic exoenzymes
Functioning in DNA and cell wall synthesis Bearing the receptors of
the chemotactic and other sensory transduction systems
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- Bacterial cell structure Cell membrane Mesosome: Folded
invaginations in the cytoplasmic membrane Bind and pull apart
daughter chromosomes during cell division
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- Bacterial cell structure Cell membrane Transport of substances
1. Passive transport Simple diffusion, faciliated diffusion,
channel proteins 2. Active transport Ion-coupled transport,
ATP-binding cassette (ABC) transport 3. Group translocation 4.
Special transport process
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- Bacterial cell structure Cell membrane Transport of substances
1. Passive transport: (Diffusion; no energy) A. Simple diffusion:
Not selective; (eg, dissolved O 2, CO 2, and H 2 O) B. Faciliated
diffusion: Selective C. Channel proteins: Rare in prokaryotes;
selective channels passage of specific molecules (eg,
glycerol)
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- Bacterial cell structure Cell membrane Transport of substances
1. Passive transport: (Diffusion; no energy)
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- Bacterial cell structure Cell membrane Transport of substances
2. Active transport: A. Ion-coupled transport: I. Uniport: single
transport of a solute II. Symport: cotransport of a solute and H +
in same direction III. Antiport: transport of two similar solutes
in opposite directions
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- Bacterial cell structure Cell membrane Transport of substances
2. Active transport: A. Ion-coupled transport
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- Bacterial cell structure Cell membrane Transport of substances
2. Active transport: B. ATP-binding cassette (ABC) transport: Uses
ATP Binding proteins Gram-negative bacteria periplasmic space
Gram-positive bacteria outer surface of the cell membrane
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- Bacterial cell structure Cell membrane Transport of substances
2. Active transport: B. ATP-binding cassette (ABC) transport: Bound
substrate is transferred to a membrane- bound protein complex
Hydrolysis of ATP Energy membrane pore open movement of substrate
into the cell
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- Bacterial cell structure Cell membrane Transport of substances
2. Active transport: B. ATP-binding cassette (ABC) transport
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- Bacterial cell structure Cell membrane Transport of substances
3. Group translocation: Uptake of certain sugars (glucose, mannose)
Not active transport Phosphotransferase system: Membrane carrier
protein phosphorylated (phosphoenolpyruvate) binds the free sugar
transport into the cytoplasm: sugar phosphate
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- Bacterial cell structure Cell membrane Transport of substances
3. Group translocation:
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- Bacterial cell structure Cell membrane Transport of substances
4. Special transport process: Iron (Fe): essential nutrient for
bacteria Siderophores transport Fe into the cell
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- Bacterial cell structure Cell membrane Transport of substances
4. Special transport process:
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- Bacterial cell structure Cytoplasmic structures Nucleoid
Ribosome Cytoplasmic membrane Cell wall External structures
Cytoplasmic structures Nucleoid Ribosome Cytoplasmic membrane Cell
wall External structures
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- Bacterial cell structure Cell wall Distinguish Gram-positive
from Gram-negative bacteria Most prokaryotes Peptidoglycan (murein)
layer Rigidity, and the shape of the bacterial cell
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- Bacterial cell structure Cell wall
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- Gram-positive bacteria Peptidoglycan Teichoic acid Lipoteichoic
acid Gram-positive bacteria Peptidoglycan Teichoic acid
Lipoteichoic acid Gram-negative bacteria Peptidoglycan Periplasmic
space Outer membrane Proteins Lipopolysaccharide Gram-negative
bacteria Peptidoglycan Periplasmic space Outer membrane Proteins
Lipopolysaccharide
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- Bacterial cell structure Cell wall Peptidoglycan Gram-positive
bacteria: Thick peptidoglycan; ~40 sheets (50% of the cell wall)
Gram-negative bacteria: Thin peptidoglycan; 1 or 2 sheets (5-10% of
the cell wall)
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- Bacterial cell structure Cell wall Peptidoglycan Peptidoglycan
layer; Provides the strength to the bacterial cell wall Provides
the osmotic stability to the bacterial cell Synonyms: Murein,
mucopeptide
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- Bacterial cell structure Cell wall Peptidoglycan Lysozyme
(enzyme in tears, saliva and nasal secretions) degrades the
peptidoglycan Hypotonic media Osmotic pressure differences water
flows into the cell cell lysis
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- Bacterial cell structure Cell wall Peptidoglycan Isotonic
media: Gram-positive bacteria Lysozyme Protoplasts Gram-negative
bacteria EDTA-lysozyme Spheroplasts If protoplasts/spheroplasts are
able to grow and divide, they are called L-forms.
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- Bacterial cell structure Cell wall Peptidoglycan Lysozyme
treatment protoplasts
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Peptidoglycan: Glycan portion: N-acetylglucosamine (GlcNAc, NAG)
N-acetylmuramic acid (MurNAc, NAM) Peptide portion: Tetrapeptide
side chains Peptide cross-bridges Peptidoglycan: Glycan portion:
N-acetylglucosamine (GlcNAc, NAG) N-acetylmuramic acid (MurNAc,
NAM) Peptide portion: Tetrapeptide side chains Peptide
cross-bridges
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transglycosylation: NAM-NAG are linked together ( -1,4 glycosidic
bond) Enzyme: Transglycosylase
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transpeptidation: Peptide chains attach to N-acetylmuramic acid
Enzyme: Transpeptidase
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transpeptidation: Pentapeptide: L-Alanine (L-Ala) D-Glutamate
(D-Glu) L-Lysine (L-Lys) / Diaminopimelic acid (DAP) D-Alanine
(D-Ala)
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transpeptidation: Pentapeptide: The terminal D-Alanine (D-Ala) from
pentapeptide is removed by transpeptidase and carboxypeptidase
enzymes In mature peptidoglycan, peptide chains are
tetrapeptides
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transglycosylase, transpeptidase and carboxypeptidase enzymes are
called Penicillin-binding proteins (PBPs)
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transpeptidation: Gram-negative bacteria: Diaminopimelic acid of
one tetrapeptide and terminal D-alanine of second tetrapeptide are
directly linked
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
Transpeptidation: Most Gram-positive bacteria: L-lysine of one
tetrapeptide and D-alanine of second tetrapeptide are linked by
pentaglycine (Gly 5 ) cross-bridge
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- Bacterial cell structure Cell wall Peptidoglycan synthesis
L-Ala D-Glu DAP / L-Lys D-Ala Gly 5
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- Bacterial cell structure Cell wall Teichoic acid / Lipoteichoic
acid Gram-positive bacteria Common surface antigens (distinguish
bacterial serotypes) Attachment (adherence) to the host cell
Important factors in virulence Teichoic acids peptidoglycan
Lipoteichoic acids cytoplasmic membrane
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- Bacterial cell structure Cell wall Teichoic acid / Lipoteichoic
acid
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- Bacterial cell structure Cell wall Periplasmic space
Gram-negative bacteria The space between the inner and outer
membranes Contains the peptidoglycan layer Possess hydrolytic
enzymes (proteases, lipases,...) (breakdown of large molecules for
metabolism)
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- Bacterial cell structure Cell wall Periplasmic space
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- Bacterial cell structure Cell wall Outer membrane Gram-negative
bacteria Bilayered structure: Inner leaflet similar composition
with the cell membrane Outer leaflet contains lipopolysaccharide
(LPS)
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- Bacterial cell structure Cell wall Outer membrane
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- Exclude hydrophobic molecules (unusual feature among biological
membranes!) Protect the bacterium (eg, digestive system) Connected
to both the peptidoglycan layer and the cytoplasmic membrane
Lipoprotein: connects peptidoglycan with outer membrane
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- Bacterial cell structure Cell wall Outer membrane Possess
special channels (porins): passive diffusion of
low-molecular-weight hydrophilic compounds (sugars, amino acids and
ions) Large antibiotic molecules penetrate slowly: antibiotic
resistance!
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- Bacterial cell structure Cell wall Outer membrane
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- Bacterial cell structure Cell wall Lipopolysaccharide
Lipopolysaccharide (LPS) Endotoxin of Gram-negative bacteria
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- Bacterial cell structure Cell wall Lipopolysaccharide
O-specific polysaccharide: Induces specific immunity (O-antigen)
Common core polysaccharide: Same in all Gram- negative bacteria
Lipid A: Responsible for primary toxicity O-specific
polysaccharide: Induces specific immunity (O-antigen) Common core
polysaccharide: Same in all Gram- negative bacteria Lipid A:
Responsible for primary toxicity
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- Bacterial cell structure Cytoplasmic structures Nucleoid
Ribosome Cytoplasmic membrane Cell wall External structures
Cytoplasmic structures Nucleoid Ribosome Cytoplasmic membrane Cell
wall External structures
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- Bacterial cell structure External structures Capsule/slime
layer Flagella Fimbriae (pili)
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- Bacterial cell structure External structures Capsule/slime
layer Distinct bacterial species Polysaccharide Capsule of Bacillus
anthracis Polypeptide (poly-D-glutamic acid)
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- Bacterial cell structure External structures Capsule/slime
layer Capsule condensed layer; closely surrounds the bacterium
Slime layer loosely adherent; nonuniform in density and thickness
Capsule/slime layer: also called glycocalyx
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- Bacterial cell structure External structures Capsule/slime
layer Protects bacteria against phagocytosis
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- Bacterial cell structure External structures Capsule/slime
layer Plays a role in adherence (biofilm formation) Artificial
valves, catheters,
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- Bacterial cell structure External structures Capsule/slime
layer Flagella Fimbriae (pili)
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- Bacterial cell structure External structures Flagella
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- Thread-like appendages Composed of protein subunits called
flagellin Subunits aggregate and form a helical structure Highly
antigenic (H antigens) If removed by mechanical agitating; new
flagella are rapidly formed and motility is rapidly restored
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- Bacterial cell structure External structures Flagella Types of
arrangements of flagella: Monotrichous single polar flagellum
Amphitrichous single polar flagella opposite sites Lophotrichous
multiple polar flagella opposite sites Peritrichous flagella
distributed over the entire cell
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- Bacterial cell structure External structures Flagella
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- Hook: Short curved structure Joint between the basal body and
the flagellum Basal body: Set of rings 1 pair (M-S ring) in Gram-
positive bacteria; 2 pairs (L-P, M-S) in Gram- negative
bacteria
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- Bacterial cell structure External structures Flagella
Gram-negativeGram-positive
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- Bacterial cell structure External structures Flagella
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- Electric field and proton gradient across the membrane: Proton
motive force Flow of protons through the motor; From the
periplasmic space, to the cell membrane and the cytoplasm
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- Bacterial cell structure External structures Flagella
Chemotaxis: Moving toward (run, swim) food and away (tumble)
poisons Rotation of the flagellum: Counterclockwise (run);
clockwise (tumble)
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- Bacterial cell structure External structures Flagella
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- Bacterial cell structure External structures Capsule/slime
layer Flagella Fimbriae (pili)
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- Bacterial cell structure External structures Fimbriae (pili)
Gram-negative bacteria Shorter and finer than flagella Composed of
protein subunits called pilins Adhesins: minor proteins at the tips
of pili; responsible for attachment
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- Bacterial cell structure External structures Fimbriae (pili)
Ordinary pili: Adherence of bacteria to host cells Sex pili:
Attachment of donor and recipient cells in bacterial
conjugation
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- Bacterial cell structure Endospores (spores) Distinct bacterial
genera; the most commons: Bacillus (Gram-positive aerobic rod)
Clostridium (Gram- positive anaerobic rod) Response to
environmental conditions (depletion of nutrients)
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- Bacterial cell structure Endospores (spores) Cannot be stained
with Gram (seen colourless) BacillusClostridium Spore
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- Bacterial cell structure Endospores (spores) Special staining
techniques (eg, malachite green stain) Bacillus Spore
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- Bacterial cell structure Endospores (spores) Sporulation
formation of spore Liberated when the mother cell undergoes
autolysis Resting cell; highly resistant to desiccation, heat, and
chemical agents Germination favorable nutritional conditions;
activation of spore to produce a single vegetative cell
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- Bacterial cell structure Endospores (spores) Sporulation
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- Bacterial cell structure Endospores (spores) Parts of spores
(from in to outwards): Core Spore wall Cortex Coat Exosporium
Core
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- Bacterial cell structure Endospores (spores) Core The core: is
the spore protoplast Contains chromosome Does not contain ATP
(energy of germination is stored as 3-phosphoglycerate) Heat
resistance of spores; Dehydrated state Calcium dipicolinate found
in the core
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- Bacterial cell structure Endospores (spores) Spore wall Spore
wall: Contains normal peptidoglycan Becomes the cell wall of the
germinating vegetative cell
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- Bacterial cell structure Endospores (spores) Cortex Cortex: The
thickest layer of the spore envelope Contains an unusual type of
peptidoglycan Fewer cross-links Extremely sensitive to lysozyme
Autolysis plays a role in spore germination
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- Bacterial cell structure Endospores (spores) Coat Coat:
Composed of a keratin-like protein Impermeable resistance of spores
against antibacterial chemical agents
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- Bacterial cell structure Endospores (spores) Exosporium
Exosporium: The outermost layer of spore envelope Composed of
proteins, lipids, and carbohydrates Consists of a paracrystalline
basal layer and a hairlike outer region
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- Bacterial cell structure Classification Gram-staining feature
Gram-positive Gram-negative Morphology Coccus, bacillus,
coccobacillus,
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- Bacterial cell structure Classification Gram staining
Introduced by Hans Christian Joachim Gram Based on the differences
of Gram-positive and Gram-negative cell wall
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- Bacterial cell structure Classification Gram staining Basic
principle: Crystal violet gets trapped in the thick and
cross-linked peptidoglycan of Gram-positive bacteria Gram-negative
bacteria (thin peptidoglycan) are easily decolorized by alcohol and
do not retain crystal violet
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- Bacterial cell structure Gram staining Crystal violet Lugol
(iodine) Alcohol Safranin (fuchsin) Crystal violet Lugol (iodine)
Alcohol Safranin (fuchsin)
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- Bacterial cell structure Classification Gram staining
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- Gram-positiveGram-negative
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- Bacterial cell structure Classification Morphology (basic)
Coccus spherical Bacillus rod-shaped Coccobacillus transition
form
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- Bacterial cell structure Classification Morphology
Gram-positive cocci Gram-negative cocci
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- Bacterial cell structure Classification Morphology
Gram-positive bacilli Gram-negative bacilli
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- Bacterial cell structure Classification Morphology
Gram-negative coccobacilli