1
Q
What are the cons of intracellular survival?
A
- Must overcome host barriers
- Must modulate innate immunity
- Must modulate cell-mediated immunity
- Must overcome bactericidal stress
2
Q
What are the pros of intracellular survival?
A
- Gain access to a protected / nutritious environment -> has a lot of carbon sources
- Some protection from the immune response
- Have time to adapt and modify the environment in the cell
3
Q
How are intracellular pathogens grouped?
A
- Facultative intracellular pathogens vs. obligate intracellular pathogens
- Growth and survival in phagocytic cells after phagocytosis vs. growth and survival in non-phagocytic cells through induced uptake
4
Q
Name some examples of facultative intracellular pathogens
A
- Salmonella sp.
- Legionella
- Shigella sp. -> dysentry
- Yersinia sp. -> plague / gastroenteritis
5
Q
Name some examples of obligate intracellular pathogens
A
- Mycobacterium sp.
- Chlamydia sp. -> pneumonia / genital infections
6
Q
Name some examples of bacteria that grow and survive in phagocytic cells
A
- Salmonella -> typhoid fever / gastroenteritis
- Listeria monocytogenes -> listeriosis
- Mycobacterium sp. -> TB / leprosy
- Legionella pneumophila -> legionnaires disease
7
Q
Name some examples of bacteria that grow and survive in non-phagocytic cells
A
- Salmonella -> will infect gut epithelial cells
- Shigella
- Listeria
8
Q
Describe the appearance of macrophages
A
Large mononuclear cells with granular cytoplasm
9
Q
Where are Kupffer cells found?
A
Liver
10
Q
Where are alveolar macrophages found?
A
Lungs
11
Q
Where are osteoclasts found?
A
Bone
12
Q
Where are microglia found?
A
Brain
13
Q
What do macrophages require for activation?
A
IFN gamma
14
Q
Where do macrophages migrate after killing?
A
Lymph nodes
15
Q
Describe the appearance of neutrophils
A
Small with multilobed nucleus and granular cytoplasm
16
Q
What do neutrophils do after killing?
A
Die at the site by apoptosis
17
Q
What receptors do macrophages express for bacterial constituents?
A
- Mannose receptor
- LPS receptor
- Glucan receptor
18
Q
What type of bacteria does the LPS receptor detect?
A
Used for gram negative bacteria
19
Q
What happens when bacteria bind to macrophage receptors?
A
- Initiates the release of cytokines and small lipid mediators of inflammation -> particularly if TLR4 is bound
- Internalisation of pathogen into the phagosome
- Acidification of the phagosome
- Fusion of the phagosome with lysosomes / granules containing antimicrobial compounds to form the phagolysosome
- Oxygen and nitrogen species are generated
20
Q
What pH does the phagosome reach when acidified?
A
3.5 - 4
21
Q
What do TLRs recognise?
A
Pathogen-associated molecular patterns (PAMPs)
22
Q
What does TLR binding on macrophages result in?
A
Cytokine production and cellular activation
23
Q
Name the intracellular effector mechanisms of phagocytes
A
- Acidification
- Toxic oxygen-derived products
- Toxic nitrogen oxides
- Antimicrobial peptides
- Enzymes
- Competitors
24
Q
What enzymes help bacterial breakdown in phagocytes?
A
- Lysozymes
- Acid hydrolases
- Collagenases
25
What competitors are used in phagocytes?
- Lactoferrin
| - Vitamin B12-binding protein
26
Compare the mechanisms of pathogen destruction that macrophages and neutrophils use
- Both use phagosome acidification
- Neutrophils use primary and secondary granules
- Macrophages use lysosomes
- Both use oxygen-dependent mechanisms and oxygen-independent mechanisms
- Both use nitrogen-dependent mechanisms
27
What are RNIs produced from?
L-arginine
28
What enzyme is used to produce RNIs?
Inducible nitric oxide synthase (iNOS)
29
How do intracellular bacteria avoid destruction by RNIs?
Break down L-arginine using arginases to prevent RNIs being formed
30
What enzyme is used to produce ROIs?
NADPH oxidase
31
What enzyme makes hypochlorous acid and singlet oxygen?
Myeloperoxidase
32
What are the strategies for intracellular survival in phagocytes?
- Avoid or prevent phagocytosis if unable to survive intracellularly
- Internalised but able to proliferate in the vacuole -> disable / resist killing mechanisms
- Internalised by phagocytosis but can escape the vacuole and survive in the cytoplasm
33
How does Haemophilus Influenza avoid phagocytosis?
Has a polysaccharide coat that prevents the virus being taken up by phagocytosis
34
Is Salmonella gram positive or gram negative?
Gram negative
35
What cells does Salmonella infect intracellularly?
Phagocytes and non-phagocytic epithelial cells
36
Where does Salmonella survive in phagocytes?
Survives and modifies the phagosome
37
Does Shigella stay in the phagosome after being taken up by phagocytosis?
No, it escapes the phagosome
38
Does Shigella have intracellular motility?
Yes, it can propel itself around the cytoplasm
39
Name the diseases Salmonella can cause
- Typhoid fever
- Enteric fever
- Non-typhoidal salmonellosis
40
What Salmonella causes typhoid fever?
S. typhi
41
What occurs in the first phase of typhoid fever?
- Slow fever
- Rose spots
- Mild bacteraemia
42
What occurs in the second phase of typhoid fever?
- Organism reaches the gall bladder
- Re-invasion of the intestine
- Ulcers
- Haemorrhage
- Typhoid state
- Muttering delirium or coma vigil
- Death (20%)
43
What Salmonella causes enteric fever?
S. paratyphi
44
What Salmonella causes non-typhoidal salmonellosis?
- S. typhimurium
- S. enteriditis
- S. heidelberg
- S. newport
45
What is the incubation period of non-typhoidal salmonellosis?
Usually 12-36 hours
46
What are the symptoms of non-typhoidal salmonellosis?
- Chills/fever
- Nausea/vomiting
- Abdominal pain
- Diarrhoea
47
How long does non-typhoidal salmonellosis last?
1-7 days
48
How is Salmonella transmitted?
- Chicken
- Pork and beef products
- Eggs
- Some fresh produce
- Some reptiles act as vectors
49
When did the common ancestor of Salmonella exist?
25-40 million years ago
50
What separated Salmonella and Escherichia lineages?
Acquisition of Salmonella pathogenicity island 1 and the ability to cause intestinal infections
51
What are the 2 species of Salmonella?
- S. enterica
| - S. bongori
52
What divided Salmonella into the 2 species?
Acquisition of SPI2
53
How does Salmonella translocate the gut lumen?
- Induces uptake into epithelial cells in the gut
| - Can break down tight junctions between epithelial cells
54
Describe the interaction between Salmonella and macrophages
- Taken up by macrophages where it can survive and disseminate
- Once taken into the phagosome it's known as salmonella containing vesicle
- Can induce apoptosis in macrophages inducing IL-1beta and inflammation
- If released from macrophages can induce uptake into epithelial cells via the basolateral side
- Ruffling occurs as the actin cytoskeleton of the macrophage is modified by the Salmonella
55
Describe the mechanism of Salmonella invasion
- T3SS translocates effectors into the host cytoplasm which activates host Rho GTPases
- Effectors modulate the environment within the cell which leads to actin rearrangement (ruffling) and induction of mitogen-activated protein kinase paths destabilising tight junctions
- Further changes in the actin cytoskeleton made via actin-binding proteins SipA and SipC leading to bacterial uptake
- MAPK signalling activates host AP-1 and nuclear factor-kappaB causing the cell to release IL-8
- SipB induces macrophage apoptosis and IL-1 and IL-18 release leading to further destabilisation of tight junctions allowing for more bacterial passage and brings more cells for the bacteria to infect
- SptP leads to restoration of the actin cytoskeleton and down-modulating MAPK signalling and inflammation
- SspH1 and AvrA also inhibit NF-kappaB
56
How does Salmonella survive the macrophage?
- Salmonella produces arginase II that breaks down L-arginine to prevent the production of RNIs
- SPI-2 and PhoPQ are involved in the evasion of ROIs, SCV is also involved in this
- Salmonella induces the TLR to create an activated state
- Salmonella inhibits fusion of the lysosome with the SCV to prevent the breakdown of Salmonella
- Salmonella pushes the macrophage to go to an M2 phenotype which produces more anti-inflammatory cytokines
- Salmonella promotes pyroptosis, apoptosis, autophagy or necroptosis which are tyes of cell death the Salmonella can survive
- Pyroptosis is caspase1 mediated and produces IL-1beta and IL-18
- Necroptosis is characterised by IFNR and RIP 1,3
- SipB promotes autophagy
