Lecture 5: Bacterial Cell Envelope Part 1 Flashcards
In order to colonise/infect, a pathogen must:
- Gain access to host
- Adhere to host surfaces
- Evade host defenses
Gram-negative cell envelope inner and outer membrane:
Inner:
- inner faces towards cytoplasm
- outer faces away from cytoplasm
- composed of phospholipid bilayers
Outer:
- phospholipid inner face
- LPS (lipo polysaccharide) in outer face
Function of outer membrane
- Structural role : mechanical stability
- Defensive layer : protects against antibiotics, bacteriophages, antimicrobial peptides
- Permeability barrier
What is LPS comprised of?
- Lipid A, imbedded in membrane
- Core, oligosaccharide
- O antigen
What is LPS comprised of?
- Lipid A, imbedded in membrane
- Core, oligosaccharide
- O antigen
Structure of LPS
- O antigen, 3-5 sugars repeated <25 times
- Core oligosaccharide Glc - D-Galactose Gal - D-Glucose Hep - Heptose KDO - Keto-deoxyoctanate
- Lipid A, resides in outer membrane, endotoxin & proinflammatory
Modification of LPS
Can modify structure to:
Dampen proinflammatory immune responses
or provide resistance to cationic antimicrobial peptides (CAMPs)
Ex- Vibrio cholerae - Glycine modifies lipid A
What is proinflammatory?
Interacts with receptors on macrophages and B-cells leading to cytokine release - endotoxic shock
Gram-positive cell envelope comprised of:
- Teichoic acids
2. Covalently bound proteins
Function of Teichoic Acid
- Binding to receptors and surfaces
- Neg surface charge
- Growth and division
- Host cell recognition
- Protect from harmful molecules : AMPS, Glycopeptide antibiotics
Modification to T. Acids
- backbone polymer relatively conserved within species
- lots variation in modification
D-Alanine: increase resistance to host defenses, antimicrobial peptides, glycopeptide antibiotics
Glycosylation: increase protection from immune system
Describe Teichoic Acid
are negatively charger polymers
can be wall teichoic acid and in cell wall
or lipoteichoic acid and imbedded in cytoplasmic membrane
Describe Covalently bound proteins
Cell wall anchored proteins and pili synthesised in cytoplasm
Translocated across cytoplasmic membrane (secretion)
Became covalently anchored to peptidoglycan and displayed on bacterial surface
Key role in attachment and adhesion
Function of sortase-anchored surface proteins
Bacterial adhesion (cell, extracellular matrix components) Invasion of mammalian cells Binding to plasma proteins Immune evasion Inducing inflammatory Biofilm formation
