Kachur - Topic 2 - Bacterial Structure

Question 1

What is peptidoglycan?

Answer 1

• repeating disaccharide of NAG and NAM

Question 2

What is NAG

Answer 2

• N-acetyl glucosamine
• a monosaccharide derivative of glucose
• amide between glucosamine and acetic acid

Question 3

What is NAM

Answer 3

• N-acetyl muramic acid
• monosaccharide derivative of NAM

Question 4

How are NAG and NAM cross-linked

Answer 4

with oligopeptides at the lactic acid residue of NAM

Question 5

How do crosslinking peptides between gram positive and gram negative differ

Answer 5

Gram pos
- 9-15 aa
- often pentaglycine cross link
Gram neg
- 2 aa crosslink
- tetrapeptide links directly to another tetrapeptide

Question 6

What is special about the D isomer of amino acids

Answer 6

• uncommon in nature
• used in bacteria to avoid protease digestion
• key to regulating disease
• connects through lysine component

Question 7

What is N. gonorrhea?

Answer 7

• gram negative
• highly cross-linked -> harder to break down
• resistant to some antibiotics

Question 8

What is the lipopolysaccharide layer?

Answer 8

• major component of the outer membrane of Gram negative bacteria
• elicit strong immune responses (O antigen can induce strong immune responses)
• LPS contribute greatly to the structural integrity of the bacteria and protecting the membrane from chemical attacks

Question 9

How does LPS affect the charge of the cell membrane

Answer 9

• LPS also increases the negative charge of the cell membrane and helps stabilize the overall membrane structure
• LPS requires association with divalent cations (Mg++) to neutralize charge repulsion

Question 10

What are the 3 molecular domains of LPS?

Answer 10

• lipid A
• the core
• the O-antigen

Question 11

What are the non-essential components of the LPS

Answer 11

• the core and the O antigen

Question 12

What is Lipid A?

Answer 12

• phosphorylated glucosamine disaccharide with associated fatty acids
• 4-6 fatty acids tails
• allows bilayer formation
• antigenic
• bacteria can function with only Lipid A

Question 13

What is the core?

Answer 13

• attached directly to Lipid A
• mostly sugar but can contain amino acids
• diverse

Question 14

What is Kdo?

Answer 14

the most common sugar in LPS

Question 15

What is the O-antigen

Answer 15

attached to core olysaccharide
- highly diverse
- often determines strain type

Question 16

What is the difference between rough and smooth LPS?

Answer 16

• rough O antigen generally associate with non-pathogens (less variable, usually less resistant to antibiotics)
• smooth can generally be more virulent than rough
• long O antigens are associated with virulence

Question 17

What is the lipid A domain responsible for

Answer 17

toxicity of the gram negative bacteria
- upon bacterial lysis by the immune system, fragments containing lipid A are released into circulation causing:
- fever, diarrhea and endotoxic shock

Question 18

What are the different types of PAMPS

Answer 18

• peptidoglycan
• lipid A
• teichoic acid
• capsules
• these are all unique to bacteria -> allow host detection

Question 19

What are toll-like receptors (TLRs)?

Answer 19

• recognize PAMPs
• expressed in all cells of innate immune system (either on cell surface or endosomes)
• when a TLR is bound by a ligand, it activates a signalling cascade that initiates the release of pro-inflammatory cytokines

Question 20

What is TLR6?

Answer 20

• recognizes peptidoglycan in gram +
• recognizes lipoteichoic acid in gram +
• recognize lipoproteins of gram -

Question 21

What is TLR4?

Answer 21

• recognizes LPS in gram -
• found on cell surface

Question 22

What is TLR3?

Answer 22

• found in endosomes
• detects intracellular + phagocytosed pathogens

Question 23

What are NODs

Answer 23

• nucelotide-binding domain, leucine rich-repeat - containing receptors)
• sensors of intracellular PAMPS
• overlap between TLR cascades and NOD cascades

Question 24

What is the pathogen profile of helicobacter pylori?

Answer 24

• gram negative
• acid tolerant
• infects lining of gut (asymptomatic)
• cause acute gastritis + chronic inflammation (ulcers)
• survives in the gut by secreting a base to neutralize acid + liquify mucus
• flagellar bundle: spirochaete shape allows it to penetrate mucus layer

Question 25

What does NOD 1 recognize?

Answer 25

a modified dipeptide commonly found in gram negative

Question 26

What does NOD 2 recognize?

Answer 26

peptidoglycan in both gram + and gram -

Question 27

What is the pathogen profile of Listeria monocytogenes?

Answer 27

- gram negative - causes listeriosis: serious infection usually caused by eating contaminated food - likely to sicken pregnant women and their newborns, adults aged 65 or older and people with weakened immune systems - can grow 0-37 degrees Celcius - present in soft cheeses + raw milk - attached to host via D-galactose (sugar on surface) - can survive in phagocytes + can manipulate host cytoskeleton

Question 28

How does Lm evade NLR recognition

Answer 28

50% of NAG replaced by glucosamine through deacetylation by the PgdA enzyme

Question 29

What are some modifications in the cell envelope that help Lm evade NLR recognition

Answer 29

1. Deacetylation of NAG by PgdA 2. Glycosylation of teichoic acid = mechanism that enhances virulence is unknown 3. Lysine is added to cell walls to increase + charge 4. Adaptation for virulence => enhancing + charges which allows avoidance of cationic AMPs

Question 30

Why are lipid A modifications important

Answer 30

essential to evade AMPs and TLR4

Question 31

What are evasion strategies of Helicobacter pylori that promote survival in the host

Answer 31

1. Dephosphorylation = removes (-) charge, resistant to CAMPs 2. Removal of (-) charge by adding amine 3. 2 fewer HC tails: hexacylated lipid A is highly antigenic

Question 32

What are evasion strategies of Yersinia pestis that promote survival in the host

Answer 32

- when residing in the flea vector, Y. pestis produces an endotoxic hexa-acylated lipid A that is a strong immunostimulant in humans - temperature change from fleas in humans causes changes in gene expression => turns on virulence genes - in fleas = hexacylated lipid A is antigenic but not to flea - Yersinia is virulent at 37 degrees - enzyme is activated with temp shift that cleaves 2 acyl chains = TLR4 evasive

Question 33

What are evasion strategies of Vibrio cholera

Answer 33

water borne illness that exists in copepod reservoirs - addition of a diglycine to Lipid A decreases AMP sensitivity

Question 34

What are antimicrobial peptides?

Answer 34

- potent members of the innate immune response - have been shown to kill gram-negative and gram-positive bacteria

Question 35

What are different subgroups of antimicrobial peptides?

Answer 35

- alpha helices - beta sheets - mixture of alpha and beta - cyclic - extended

Question 36

What is Kalata B2?

Answer 36

- found in plants - shown to have insecticidal, antitumor, antimicrobial

Question 37

What are the three models of action mechanisms by AMPs

Answer 37

A) Barrel-Stave model: AMP inserts perpendicularly B) Carpet model: small areas of membrane are coated in AMPs C) Torodial pore model: represents Barrel Stave except AMP associates with phospholipid head