CTE2 - bacteriology

Question 1

PRRs and effects

Answer 1

• TLRs –> MyD88 (NfkB) TRIF (IFN)
• Complemenet receptors (CR3) –> co-stimulation/phagocytosis
• Scavenger –> phagocytosis
• Formyl peptide receptor –> chemoattraction
• NK cell recptors (KIRs) –> NK activation
• C-type lectin receptors –> Th17(dectin-fungi) phagocytosis (mannose receptor)
• soluble lectin receptors –> complement activation and opsonisation

Question 2

koch’s postulates

Answer 2

1. microbe must be present during disease
2. must be isolated and grown pure in culture
3. when cultured microorganism is applied to other organism it must get disease
4. must be isolated from inoculated and now diseased host and be identical to step 2

Question 3

tolerance by exclusion (intestine)

Answer 3

• Firm mucus layer and AMPs, sIgA prevent access to epithelial cells
• Commensals can further strengthen these barriers
• Anti-inflammatory properties of commensal metabolites (SCFAs)
• PAMP-modifications: commensal lipidA less toxic
• Damage requirement: PAMP in combination with DAMP activate Inflammasome
• Compartmentalization of PRRs:
  -TLR4-expression only on IECs in crypts
  -TLR5 on basolateral side of IECs
  
  • NLR in cytosol

Question 4

tolerance by constraint

Answer 4

• Certain commensals can block NfkB pathway via two main mechanisms:
  o Promoting the nuclear export of NF-kB through PPAR-g signalling
  o Inhibiting the polyubiquitination of IkB, or preventing IkB phosphorylation
   Salmonellae and Lactobacillus (prevent ubiquitin)
   Yersinia spp. (prevent phosphorylation)

Question 5

NFkB pathway

Answer 5

1. PAMP - TLR
2. MyD88
3. activation the IkB–kinase complex (IkK)
4. Phosphorylation of IkB (the inhibitor of transcription factor NF-kB).
5. IkB is then polyubiquitinated and subsequently degraded by a proteasome
6. Releasing the transcription factor NF-kB for nuclear localization where it mediates pro-inflammatory gene expression.

Question 6

phagocytosis

Answer 6

1. In the process of phagocytosis, the cell takes up microbes via (complement, scavenger, Fc, lectin) receptors on its plasma membrane. pH=7.4
2. The microbe is then present inside the cell in a phagosome. pH=5.5-6.5
3. The phagosome then fuses with a lysosome (pH=4.5) and becomes a phagolysosome. pH=5
4. Inside the phagolysosome microbes are killed by ROS, NO and lysosomal enzymes. pH=5

Question 7

evasion of phagocytosis

Answer 7

• prevention of acidification of phagolysosome
• encapsulation
  - Capsular polysaccharides are poor immunogens
  - Capsular can consist of hyaluronic acid mimicking human connective tissue
  - Capsules are slippery -> hard to grab by phagocyte
  - Capsule protects destruction within phagolysosome
• biofilm
• resistance to lysosomal enzymes
• inhibition phagosome/lysosome fusion

Question 8

complement

Answer 8

Alternative pathway
- spontaneous lysis of C3

Classical pathway
- C1q binds to IgM, IgG, pentraxins (CRP)

Lectin pathway
- MBL binding to mannose or
- Ficolin binding to lipoteichoic acid

Question 9

evasion of complement

Answer 9

• encapsulation and biofilm
• long O-antigen (LPS)
• cleavage of C5a –> inhibit chemotaxis

Question 10

humoral effects on bacteria

Answer 10

• neutralisation
• opsonisation and phagocytosis
• complement activation
• ADCC

Question 11

evasion of Abs

Answer 11

• encapsulation and biofilm
• proteases
• antigenic masking
• antigenic variation
• intracellular growth
• binding Fc region of Abs

Question 12

M cells as invasion mode

Answer 12

• M cells express many receptors, which are more accessible due to the decreased amount of mucus and Paneth cells around the M cells.
  o β1-integrin –> Yesinia spp.
  o β1-integrin –> MAP which forms a fibronectin bridge
• E-cadherin and hepatocyte growth factor receptor (MET).
  o Listeria monocytogenesattaches to E-cadherin and MET –> intracellular actin recruitment and infection

Question 13

vibro cholerae

Answer 13

• Vibrio cholerae secretes a Zn2+-dependent metalloproteinase, called haemagglutinin protease (Hap) –> mucinolytic
  o Vibrio cholerae also produces the toxin zonula occludens toxin (ZOT), which interacts with occludin and ZO1  tight junction disruption

Question 14

clostridium

Answer 14

• Clostridium perfringens secretes enterotoxin, which acts on the tight junction protein claudin.

Question 15

giardia lablia

Answer 15

• Giardia lamblia is a protozoan that is able to degrade the mucus layer.
  o It can also reorganize cytoskeletal F-actin filaments and disrupt ZO1, which increases permeability.

Question 16

goblet cells as invasion mode

Answer 16

• L. monocytogenes can enter the epithelium via goblet cells when they have secreted their mucus.
  o When the goblet cells have secreted their mucus, the host receptor E-cadherin will become accessible.
• L. monocytogenes can bind to E-cadherin, after which it is internalized into the epithelium via transcytosis and excreted again via exocytosis

Question 17

AMP evasion

Answer 17

• S. typhimurium has the ability to change the anionic charge of its own lipid A.
  o It does this using phase variation.
  o Its goal is to reduce the negative charge by adding amino acid groups that are positively charged through aminoarabinose.
• This is beneficial for the bacterium since normally the negative charge attracts positive/cationic antimicrobial peptides (CAMPs

Question 18

salmonella virulence

Answer 18

• Can evade activity of cationic AMPs by altering
  the anionic character of the cell surface
• Use fimbriae to bind to M-cells
• T3SS injects effector molecules into cells
• Effector molecules facilitate uptake and
  intracellular survival (video)
• Remain in endocytic vacuoles

Question 19

shigella virulence

Answer 19

Uptake by M-cells
* Effector molecules facilitate uptake (membrane ruffling)
* Endocytosed by M cells -> transcytosed toward pocket -> uptake by resident macrophages
* Shigellae lyse the phagocytic vacuole and replicate in the host cell cytoplasm
* Massive inflammatory cell death of macrophages
* Subsequent released bacterial cells enter enterocytes from basolateral side –> T3SS
* Bacteria released from vacuole and replication in cytoplasm
* Shigella proliferation induces actin polymerization at one pole of the bacterium, providing the propulsive force required for intracellular movement (thus immune evasion)

Question 20

superantigens in S.aureus and S. pyogenes

Answer 20

• Superantigens are a type of exotoxin that are able to activate T cells by binding both to the TCR and MHCII on an APC, without needed an antigen to do this –> cytokine storm

o Toxin shock syndrome toxin  S. aureus
o Staphylococcus enterotoxins and erythrogenic toxin A and C  S. pyogenes