Lecture 6. Bacteria Cell Envelope Part 1 Flashcards
What must a pathogen do to colonise or infect ?
- Gain access to the host
- Adhere to host surfaces
- Evade host defences
What structures are important for adherence and immune system evasion ?
Structures within the bacterial cell
What are some functions of the outer membrane ?
- Structural role - mechanical stability
- A defense layer
- Permeability barrier
What does the outer face of the outer membrane have that the inner face does not ?
LPS replaces phospholipid in the outer face
Where is LPS located exclusively ?
Outer membrane
What is LPS essential for ?
To maintain the barrier function of the outer membrane
What does LPS do structurally ?
Forms a very tightly packed layer - strong lateral interactions between LPS molecules
What is LPS ?
A proinflammatory that interacts with receptors on macrophages and B-cells leading to cytokinase release
What can cytokinase release result in ?
Endotoxic shock
What is the structure of LPS ?
- O-Antigen
- Core oligosaccharide
- Lipid A
What is the structure of O-antigen in LPS /
3-5 sugars repeated less than 25 times
Where does lipid A reside in LPS ?
The outer membrane
What makes up the core oligosaccharide in LPS ?
- D-galactose
- D-glucose
- Heptose
- Keto-deoxyoctanate
What is lipid A responsible for ?
Endotoxin - responsible for most toxic effects caused by gram negative bacteria
What is unique about lipid A structure ?
Recognised by many different host receptors
What type of adherence do lipid A and rough LPS have ?
Bad adherence
What type of adherence do smooth LPS have ?
Good adherence
What are morphotypic differences driven by ?
Rough and smooth LPS
What can certain bacteria do to modify their LPS structure to do ?
- Dampen proinflammatory immune responses
2. Provide resistance to cationic antimicrobial peptides
What type of bacteria is Vibrio cholerae ?
Gram negative
How does the amino acid modification of lipid A confer resistance to antimicrobial peptides ?
The lipid moiety if LPS is decorated with positively charged amino acids. This removes the negative charge from lipid A increasing resistance
What can modification of lipid A do in Heliobacter pylori ?
100 fold reduced toxicity
What do gram negative cell envelopes have ?
Outer membrane and LPS
What do gram positive cell envelopes have ?
- Teichoic acids
2. Covalently bound proteins
What are teichoic acids ?
Negatively charged polymers
Why are teichoic acids negatively charged ?
Because of the presence of phosphates
What are the two types of teichoic acids ?
- Lipoteichoic
2. Wall teichoic
What are some functions of teichoic acids ?
- Host cell recognition
- Protection from harmful molecules
- Cation homeostasis
- Growth and division
- Binding to receptors and surfaces
In teichoic acids, what does d-Alanine have ?
Increased resistance to host defences, antimicrobial peptides, glycopeptide antibiotics
In teichoic acids, what does glycosylation do ?
Increased protection from immune systems
What are some effects of modifications in teichoic acids ?
- Glycosylation may increase susceptibility to bacteriophages
- D-alanine modification can reduce ability to adhere to host cells and establish an infection
What is the trade off in teichoic acid modifications ?
- Adherence and colonising potential – modifications less common in early infections
- Resistance to host antimicrobials, antibiotics etc. – modifications more common in chronic infection
Where are cell wall anchored proteins an pili synthesised ?
Cytoplasm
Where are cell wall anchored proteins and pili translated ?
Across the cytoplasmic membrane
Where do cell wall anchored proteins and pili become covalently anchored to and where are they displayed ?
- Peptidoglycan
2. Bacterial surface
What do cell wall anchored proteins and pili have a key role in ?
Attachment and adhesion
What is an important feature of staphylococcus aureus ?
Pentaglycine cross bridge
Where cell wall anchored proteins and pili covalently anchored to ?
The pentaglycine cross bridge of peptidoglycan sortase enzyme
What are some examples of sortase anchored surface proteins ?
- Listeria monocytogenes
- Staphylococci
- Streptococci
- Enterococci
What are some functions of sortase anchored surface proteins ?
- Bacterial ahesion
- Invasion of mammalian cells
- Binding to plasma proteins
- Immune evasions
- Inducing inflammation
- Biofilm formation
What does staphylococcus aureus adhere to ?
Fibrinogen, fibronectin, collagens
