Lecture 6. Bacteria Cell Envelope Part 1

Question 1

What must a pathogen do to colonise or infect ?

Answer 1

1. Gain access to the host
2. Adhere to host surfaces
3. Evade host defences

Question 2

What structures are important for adherence and immune system evasion ?

Answer 2

Structures within the bacterial cell

Question 3

What are some functions of the outer membrane ?

Answer 3

1. Structural role - mechanical stability
2. A defense layer
3. Permeability barrier

Question 4

What does the outer face of the outer membrane have that the inner face does not ?

Answer 4

LPS replaces phospholipid in the outer face

Question 5

Where is LPS located exclusively ?

Answer 5

Outer membrane

Question 6

What is LPS essential for ?

Answer 6

To maintain the barrier function of the outer membrane

Question 7

What does LPS do structurally ?

Answer 7

Forms a very tightly packed layer - strong lateral interactions between LPS molecules

Question 8

What is LPS ?

Answer 8

A proinflammatory that interacts with receptors on macrophages and B-cells leading to cytokinase release

Question 9

What can cytokinase release result in ?

Answer 9

Endotoxic shock

Question 10

What is the structure of LPS ?

Answer 10

1. O-Antigen
2. Core oligosaccharide
3. Lipid A

Question 11

What is the structure of O-antigen in LPS /

Answer 11

3-5 sugars repeated less than 25 times

Question 12

Where does lipid A reside in LPS ?

Answer 12

The outer membrane

Question 13

What makes up the core oligosaccharide in LPS ?

Answer 13

1. D-galactose
2. D-glucose
3. Heptose
4. Keto-deoxyoctanate

Question 14

What is lipid A responsible for ?

Answer 14

Endotoxin - responsible for most toxic effects caused by gram negative bacteria

Question 15

What is unique about lipid A structure ?

Answer 15

Recognised by many different host receptors

Question 16

What type of adherence do lipid A and rough LPS have ?

Answer 16

Bad adherence

Question 17

What type of adherence do smooth LPS have ?

Answer 17

Good adherence

Question 18

What are morphotypic differences driven by ?

Answer 18

Rough and smooth LPS

Question 19

What can certain bacteria do to modify their LPS structure to do ?

Answer 19

1. Dampen proinflammatory immune responses

2. Provide resistance to cationic antimicrobial peptides

Question 20

What type of bacteria is Vibrio cholerae ?

Answer 20

Gram negative

Question 21

How does the amino acid modification of lipid A confer resistance to antimicrobial peptides ?

Answer 21

The lipid moiety if LPS is decorated with positively charged amino acids. This removes the negative charge from lipid A increasing resistance

Question 22

What can modification of lipid A do in Heliobacter pylori ?

Answer 22

100 fold reduced toxicity

Question 23

What do gram negative cell envelopes have ?

Answer 23

Outer membrane and LPS

Question 24

What do gram positive cell envelopes have ?

Answer 24

1. Teichoic acids

2. Covalently bound proteins

Question 25

What are teichoic acids ?

Answer 25

Negatively charged polymers

Question 26

Why are teichoic acids negatively charged ?

Answer 26

Because of the presence of phosphates

Question 27

What are the two types of teichoic acids ?

Answer 27

1. Lipoteichoic

2. Wall teichoic

Question 28

What are some functions of teichoic acids ?

Answer 28

1. Host cell recognition
2. Protection from harmful molecules
3. Cation homeostasis
4. Growth and division
5. Binding to receptors and surfaces

Question 29

In teichoic acids, what does d-Alanine have ?

Answer 29

Increased resistance to host defences, antimicrobial peptides, glycopeptide antibiotics

Question 30

In teichoic acids, what does glycosylation do ?

Answer 30

Increased protection from immune systems

Question 31

What are some effects of modifications in teichoic acids ?

Answer 31

1. Glycosylation may increase susceptibility to bacteriophages
2. D-alanine modification can reduce ability to adhere to host cells and establish an infection

Question 32

What is the trade off in teichoic acid modifications ?

Answer 32

1. Adherence and colonising potential – modifications less common in early infections
2. Resistance to host antimicrobials, antibiotics etc. – modifications more common in chronic infection

Question 33

Where are cell wall anchored proteins an pili synthesised ?

Answer 33

Cytoplasm

Question 34

Where are cell wall anchored proteins and pili translated ?

Answer 34

Across the cytoplasmic membrane

Question 35

Where do cell wall anchored proteins and pili become covalently anchored to and where are they displayed ?

Answer 35

1. Peptidoglycan

2. Bacterial surface

Question 36

What do cell wall anchored proteins and pili have a key role in ?

Answer 36

Attachment and adhesion

Question 37

What is an important feature of staphylococcus aureus ?

Answer 37

Pentaglycine cross bridge

Question 38

Where cell wall anchored proteins and pili covalently anchored to ?

Answer 38

The pentaglycine cross bridge of peptidoglycan sortase enzyme

Question 39

What are some examples of sortase anchored surface proteins ?

Answer 39

1. Listeria monocytogenes
2. Staphylococci
3. Streptococci
4. Enterococci

Question 40

What are some functions of sortase anchored surface proteins ?

Answer 40

1. Bacterial ahesion
2. Invasion of mammalian cells
3. Binding to plasma proteins
4. Immune evasions
5. Inducing inflammation
6. Biofilm formation

Question 41

What does staphylococcus aureus adhere to ?

Answer 41

Fibrinogen, fibronectin, collagens