glycocalyx LABCONCEPT 5.1 cell wall plasma Prokaryotic Cell membrane Features Cell cytoplasm Cytoplasmic not present on all cells or cell membrane
pili
fimbriae 2 types of Bacterial Cell Walls LABFACT 5.1
Gram-positive bacteria Gram-negative bacteria
glycocalyx glycocalyx
What is peptidoglycan ?
(1) Gram-positive cell wall (2) Gram-negative cell wall Figure 3.13 Possible structure of peptidoglycan. Sugar peptidoglycan backbone
Tetrapeptide (amino acid) crossbridge
Connecting chain of amino acids LABFACT 5.1
Gram-positive bacteria
Gram-negative bacteria Gram-positive bacterial cell wall LABFACT 5.1
Appear purple following Gram Peptidoglycan layer (cell wall) staining Cytoplasmic membrane procedure
Lipoteichoic acid
Teichoic acid
Integral protein
Cell wall = thick layer of peptidoglycan Cell wall contains unique polyalcohols called teichoic acids Gram-Negative Bacterial Cell Walls LABFACT 5.1
Porin
Outer Porin membrane (sectioned) of cell wall Appear pink Peptidoglycan following Gram layer of cell wall Periplasmic space
Cytoplasmic staining membrane procedure
Phospholipid layers Lipopolysaccharide (LPS) layer, containing Integral lipid A proteins 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-Positive vs Gram-Negative Bacterial LABFACT 5.1 Cell Walls
Gram-Positive Gram-Negative Peptidoglycan PRS – THICK PRS – THIN
Outer Membrane PRS Periplasmic Space PRS - ONE PRS - TWO LPS ABS PRS (lipopolysaccharide) Porin ABS PRS Techoic Acid PRS ABS
PRS = PRESENT ABS= ABSENT How to perform Gram Staining Reaction ? LABFACT 5.2 purple Gram-positive bacteria pink Gram-negative bacteria Mechanism behind Gram Staining Reaction LABFACT 5.3
Thick peptidoglycan prevents decolorization
Thick peptidoglycan Thin peptidoglycan in cell wall in cell wall Gram Staining Method LABFACT 5.3
Primary Stain Step
Crystal Violet
Gram positive cell wall
Gram negative cell wall Gram Staining Method
Mordant Step
Gram’s Iodine Gram Staining Method
Decolorizing Step
Alcohol 25 sec Gram Staining Method
Counter Stain Step
Safranin Gram Staining
Simple/Differential Stain ? Acid Fast Bacterial Cell Wall LABCONCEPT 6.1 LABFACT 6.1
Peptidoglycan layer mycolic acid (cell wall)
Cytoplasmic membrane
Gram-positive cell wall Lipoteichoic acid
Teichoic acid
Integral Some gram positive bacteria have up to 60% protein mycolic acid (waxy lipids) which helps cells survive desiccation – called Acid Fast bacteria
Acid Fast bacteria cell wall Acid Fast Bacterial Cell Wall LABCONCEPT 6.1
Some Gram positive bacteria cannot be stained by LABFACT 6.1 Gram staining procedure
They have a waxy lipid called mycolic acid in their cell wall (60 %) mycolic acid which prevents water-soluble stains from penetrating the cell wall
Acid Fast bacteria cell wall How to perform Acid-Fast Staining Method ? Acid-Fast Staining Method Ziehl-Neelsen Method Primary Stain Step LABCONCEPT 6.2 HEAT Carbolfuchsin
Mechanism behind Acid-Fast Staining Method Acid-Fast Staining Method
Decolorizing Step Acid-Fast
Acid Alcohol
Non Acid-Fast Acid Fast Staining Method
Counter Stain Step
Methylene Blue
LABCONCEPT 7.1 Endospores LABFACT 7.1 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 Why are endospore making bacteria dangerous ? In canning industry heat is used to kill microorganisms inside cans – but endospore containing bacteria can survive heat LABFACT 7.2 Vegetative Bacterial Cell Endospore Free spore
Environmental Challenges Heat Chemical Starvation
Spore germinates Vegetative Bacterial Cell Endospore Free spore 1 1
Spore germinates
Spores are not part of bacterial reproductive cycle bacterial reproduction is 1 bacteria = 2 bacteria
1 Bacteria Endospore 1 Bacteria LABFACT 7.3
Spores are metabolically inactive with tough special cell walls
Location of endospores unique for different spore-forming bacteria Schaeffer-Fulton Staining Method for Endospores
Primary Stain Step LABFACT 7.4 Endospore containing HEAT Malachite Green
Vegetative Bacterial Cell Schaeffer Fulton Staining Method for Endospores
Decolorizing Step Endospore containing NO HEAT X Water
Vegetative Bacterial Cell Schaeffer Fulton Staining Method for Endospores
Counter Stain Step Endospore containing Endospore containing
Safranin
Vegetative Bacterial Cell Vegetative Bacterial Cell
Crystal Violet Staining LABFACT 7.5 External Structures of Bacterial Cells LABCONCEPT 8.1
glycocalyx cell wall
cell membrane bacteria
• 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 LABFACT 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 Figure 14.8 Relative virulence of some microbial pathogens. LABCONCEPT 8.2
Virulence
Degree of pathogenicity – not about severity of the disease it causes
But how easily it causes disease LABCONCEPT 8.3
Capsule enhances the ability of bacteria to cause disease – makes them more virulent Observe Capsule stained slide