LABCONCEPT 5.1 glycocalyx cell wall
Transcript of LABCONCEPT 5.1 glycocalyx cell wall
glycocalyxcell wall
plasma membrane
Cytoplasmicor cell membrane
Cell cytoplasm
fimbriae
pili
LABCONCEPT 5.1
Prokaryotic Cell
Features not present on all cells
2 types of Bacterial Cell Walls LABFACT 5.1
glycocalyx
(1) Gram-positive cell wall (2) Gram-negative cell wall
Gram-positive bacteria Gram-negative bacteria
glycocalyx
What is peptidoglycan ?
Sugarbackbone
Tetrapeptide(amino acid)crossbridge
Connecting chainof amino acids
Figure 3.13 Possible structure of peptidoglycan.
peptidoglycan
Peptidoglycan layer
(cell wall)
Gram-positive bacterial cell wall
Cytoplasmic
membrane
Teichoic acid
Lipoteichoic acid
Integral
protein
Cell wall = thick layer of peptidoglycanCell wall contains unique polyalcohols called teichoic acids
Appear purplefollowing Gram
staining procedure
LABFACT 5.1
Integral
proteins
Outer
membrane
of cell wall
Peptidoglycan
layer of cell wall
Cytoplasmic
membrane
Lipopolysaccharide
(LPS) layer, containing
lipid A
Porin
Porin
(sectioned)
Periplasmic space
Phospholipid layers
Cell wall = a thin layer of peptidoglycan + Outer membrane or OM
OM is a phospholipid bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)
OM is protective - may impede the treatment of disease
Lipid A portion of LPS can cause fever, vasodilation, inflammation, shock, and blood clotting
Gram-Negative Bacterial Cell Walls
Appear pinkfollowing Gram
staining procedure
LABFACT 5.1
Gram-Positive vs Gram-Negative Bacterial Cell Walls
Gram-Positive Gram-Negative
Peptidoglycan PRS – THICK PRS – THIN
Outer Membrane PRS
Periplasmic Space PRS - ONE PRS - TWO
LPS (lipopolysaccharide)
ABS PRS
Porin ABS PRS
Techoic Acid PRS ABS
PRS = PRESENTABS= ABSENT
LABFACT 5.1
Gram-positive bacteria
Gram-negative bacteria
How to perform Gram Staining Reaction ?
purple
pink
LABFACT 5.2
Thick peptidoglycan in cell wall
Thin peptidoglycanin cell wall
Thick peptidoglycan prevents decolorization
Mechanism behind Gram Staining Reaction LABFACT 5.3
Gram Staining Method
Crystal Violet
Primary Stain Step
Gram positive cell wall
Gram negative cell wall
LABFACT 5.3
Peptidoglycan layer
(cell wall)
Gram-positive cell wall
Cytoplasmic
membrane
Teichoic acid
Lipoteichoic acid
Integral
proteinSome gram positive bacteria have up to 60% mycolic acid (waxy lipids) which helps cells survive desiccation – called Acid Fast bacteria
Acid Fast bacteria cell wall
mycolic acid
Acid Fast Bacterial Cell Wall LABFACT 6.1
LABCONCEPT 6.1
Some Gram positive bacteria cannot be stained by Gram staining procedure
They have a waxy lipid called mycolic acid in their cell wall (60 %)
which prevents water-soluble stains from penetrating the cell wall
mycolic acid
Acid Fast bacteria cell wall
LABFACT 6.1
LABCONCEPT 6.1Acid Fast Bacterial Cell Wall
Acid-Fast Staining Method
HEAT
Carbolfuchsin
Primary Stain StepZiehl-Neelsen Method
How to perform Acid-Fast Staining Method ?
Mechanism behind Acid-Fast Staining Method
LABCONCEPT 6.2
prs in Cytoplasm of some Bacteria
• Unique structures produced by some bacteria
• Those which make endospores also make endotoxins
• E.g. bacteria causing anthrax, tetanus, gangrene
• Defensive strategy against unfavorable conditions
• Vegetative cells transform into endospores when multiple nutrients are limited
• Resistant to extreme conditions such as heat, radiation, chemicals
EndosporesLABFACT 7.1
LABCONCEPT 7.1
In canning industry heat is used to kill microorganisms inside cans – but endospore
containing bacteria can survive heat
Why are endospore making bacteria dangerous ?
Vegetative Bacterial Cell Endospore Free spore
Environmental Challenges
Heat
Chemical
Starvation
Spore germinates
LABFACT 7.2
Vegetative Bacterial Cell Endospore Free spore
Spore germinates
1 1
1 1Bacteria Bacteria
Spores are not part of bacterial reproductive cycle
Endospore
bacterial reproduction is 1 bacteria = 2 bacteria
Spores are metabolically inactive with tough special cell walls
Location of endospores unique for different
spore-forming bacteria
LABFACT 7.3
Schaeffer-Fulton Staining Method for Endospores
HEAT
Malachite Green
Primary Stain Step
Vegetative Bacterial Cell
Endospore containingLABFACT 7.4
Schaeffer Fulton Staining Method for Endospores
Water
Decolorizing Step
NO HEAT
X
Vegetative Bacterial Cell
Endospore containing
Schaeffer Fulton Staining Method for Endospores
Safranin
Vegetative Bacterial Cell
Endospore containing
Vegetative Bacterial Cell
Endospore containingCounter Stain Step
External Structures of Bacterial Cells
• Glycocalyces
• Structure - Gelatinous, sticky substance surrounding the outside of the cell. Composed of polysaccharides or polypeptides, or both
• Function 1) avoid dessication
2) adhesion,
3) protect from host defense
glycocalyx cell wall
cell membranecell membranebacteria
LABCONCEPT 8.1
A Type of Glycocalyces
(1) Capsule
• Firmly attached to cell surface
• Prevent bacteria from being recognized
by host – avoid phagocytosis by immune
cells
Capsule enhances the
ability of bacteria to
cause disease
LABFACT 8.1
Figure 14.8 Relative virulence of some microbial pathogens.
Virulence
Degree of
pathogenicity – not
about severity of
the disease it
causes
But how easily it
causes disease
LABCONCEPT 8.2