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Module 102: Infection and immunity > Pathogens > Flashcards

Pathogens Flashcards

1
Q

Pathogen

A

Microbe that causes disease

Can be taken out from infected animal and cause disease in healthy animals

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2
Q

Demonstration of the memory and antigen specific nature of the immune system

A
  1. Injection antigen A into an animal
  2. Take blood sample from animal a few weeks after.
  3. Inject more antigen A and new antigen B into the same animal.
  4. Take more blood samples a few weeks after.

When antibodies in the blood are observed, it will show primary and secondary response.
It will also show different antibodies being produced as a response to differen antigens

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3
Q

Virulence

A

The degree of pathology caused by an organism.

This is dependant on the fundamental properties of the organism.

Can be thought as a quantitative trait —> how much disease is caused

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4
Q

Pathogenicity

A

The ability of an organism to cause disease when isolated based of virulent traits.

Can be thought as the qualitative trait —> IF it causes disease.

This is dependant on the environment it’s placed in.

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5
Q

Opportunistic pathogens

A

Only causes disease when in immunocompromised patients.

Low virulence organisms become pathogens.

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6
Q

Infection

A

When an organism:

  • Enters the body
  • Increases in number of size
  • Damages the host whilst replicating

Invasion –> Replication –> Damage

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7
Q

Commensal

A

An organism that lives in or on a patient without causing an infection.

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8
Q

The main features of the immune system.

A

Has memory: primary and secondary response which are triggered by antigens.

Antigen specific: different antibodies are produced according to the antigen.

Tolerant:
Non reactivity to certain antigens not seen as harmful like; self-antigens, commensals, harmless environmental antigens (like pollen)

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9
Q

Strain of bacteria

A

Difference between the same species of bacteria

This is dependant on the cell wall of the bacteria

Taxonomical way to classify bacteria:
describes the antigen and proteins in the bacteria’s cell wall.

e.g E.coli O157: H7
Contains O and H antigen.

S.pyogenes M3T3
Contains M and T protein

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10
Q

Different shapes of bacteria

A

Coccus/ Cocci: Round

Bacilli/ Bacillus: Long

Spiral/ branched

Vibrio (comma shape)

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11
Q

Gram positive baceteria

A

Bacteria that turns purple when Gram stain is used:

Contains a thick peptidoglycan in the cell wall
Contains lipoteichoic and teichoic acid in cell wall

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12
Q

Gram negative bacteria

A

Bacteria that turns pink with Gram stain, very little peptidoglycan in cell wall:

Contains two lipid bilayer in the cell membrane:
Bilayer –> Thin peptidoglycan –> Second bilayer

Outer membrane contains lipopolysaccharides and proteins + pores.

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13
Q

Describe the Gram staining technique.

A
  1. Bacteria is fixed and treated with crystal violet and iodine.
  2. Decolourise the sample with alcohol.
  3. If the colour stays purple = Gram positive.
  4. If decolourisation occurs, stain with safranin. A pink colour indicates Gram negative
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14
Q

Bacterias that cannot be tested through Gram staining

A

Mycoplasma (causes pneumonia) and Chlamydia:
Do not have cell wall.

Mycobacteria: does not stain with Gram, despite having a cell wall

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15
Q

Lipopolysaccharide

A

Also known as endotoxins

Found on the outer membrane of Gram negative bacteria.

This causes a systemic activation of the immune response as the immune system is very sensitive to it.

Toll like receptors in the immune system recognises endotoxins.

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16
Q

Peptidoglycan

A

3-D polymer

Contains:
N-acetylated sugars; glucosamine and muramic acid.

3-5 amino acid peptides; resistant to enzymatic destruction.

Cross linked by transpeptidase enzymes.

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17
Q

Patterns of bacterial growth

A

Clusters: ‘Staph’ bacteria.

Chains: ‘Strep’ bacteria.

18
Q

Peptidoglycan synthesis in bacteria

A
  1. Polymerisation of N-acetylated sugars: makes the backbone of the molecule.
  2. Elongation of amino acid side changes:
    Peptides are added to sugar backbone
  3. Addition of interpeptide bridges:
    Transpeptidase enzymes add cross links between amino acids.
19
Q

Mycobacteria

A

Bacteria that does not stain with Gram:
Thick lipid layer is anchored to peptidoglycan

Has the structure of a Gram+ bacteria.

Causes:
TB, M.tuberculosis
Leprosy M.leprae

20
Q

Capsule

A

External feature of bacteria that hides the immunogenic cell wall.

Formed of a polysaccharide coat.

Metabolically demanding for the bacteria to produce.

Increases virulence of a bacteria.

The capsule is trickier to overcome as specific antibodies are required for the antibodies.

21
Q

Transposons

A

DNA sequence in bacteria that can move location in a genome.

Transposase binds to transposons and allows movement of the DNA sequence.

Allows between:
Genomic —> plasmid DNA
Between plasmids
Plasmid —> Genomic DNA

22
Q

Spores

A

Seed-like projections that form from some bacteria:

The spores are non-replicating and dormant.

Resistant to :
Drying
Temperature
Disinfection 
Digestion
23
Q

When does gene regulation occur during bacterial growth?

A

Lag and stationary phase

Bacteria sense their environment and later their growth and different metabolic rates.

24
Q

Ribosome in bacteria

A

70S

Subunits 50S and 30S.

25
Q

Staphylococcus aureus

A

Usually a commensal bacteria in the nose, gut or axilla but capable of being pathogenic:
20-60% of people have it inside them.

Gram positive bacteria that looks like golden colonies.

26
Q

Virulence of S.aureus

SSC

A

Surface proteins:
Adhesins- binding proteins that allow the bacteria to stick to other molecules.
Protein A: Binds to constant region of immunoglobulins and makes the bacteria look like ‘self’.

Secretion:
Toxins released that causes harm to host cells, like TSST-1.
Coagulase enzyme: promotes coagulation of blood, prevents immune system attacks.

Capsule:
Microcapsule that requires immune system to make a specific antibody.

27
Q

Toxins of S.aureus.

CEE

A

Cytotoxins:
Lyses host cells
Panton-valentine leukocidin (PVL) lyses polymorphs, like neutrophils.

Exfoliative:
Proteases which break down epidermal proteins

Enterotoxins (superantigen): Causes overreaction of immune system
Vomiting when ingested

28
Q

Adhesins of S.aureus

A

Protein A

Collagen binding protein

Fibronectin binding protein

Elastin binding protein.

29
Q

S. aureus skin infections

A

S.aureus is usually harmless in the nose but when it breaks through the skin, it becomes pathogenic:

Impetigo
Furunculosis
Staph abscess

30
Q

S.aureus line sepsis

A

Occurs in catheters where S.aureus bacteria crawl up the tube and forms biofilms before entering circulation of body fluids.

31
Q

S.aureus infections

A

Vascular line related infections

Epidermal infections

Bacteremia

Surgical site infections

32
Q

Toll like receptors

A

Present on monocytes/ macrophages and recognise lipopolysaccharides from Gram - bacteria.

Triggers very vigorous immune response:
Inflammation
Blood clotting
Changes in endothelial integrity

Receptors also recognise features in Gram + bacteria which trigger an immune response:
Lipoteichoic acid
Peptidoglycan

33
Q

Meningococcal septicaemia

A

Gram - bacteria that causes infection of the blood

Produces a ‘purpuric rash’:
Coagulase has been produced by the bacteria to cause clotting in blood vessels.
This produces bruises that do not disappear once glass is pressed on them (glass test).

34
Q

Meningococcal pathogenicity

A

Contains specific factors that allow it to specifically cause disease in the respiratory and meninges areas.

Adhesins
Lipopolysaccharide: It is able to sheep it’s capsule and release endotoxin
Capsule

35
Q

Staphylococcus pneumoniae virulence

A

Causes pneumonia:

Adhesin:
Specifically for respiratory mucosa.

Pneumolysin:
Toxin that binds to cholesterol and lyses features of the respiratory system like ciliated cells.

IgA protease:
Lyses imunoglobins.

Capsule:
Harder recognition and efficient phagocytosis from the immune system.
Has over 100 different types.

36
Q

Clostridium difficile

A

Gram positive bacillus bacteria:

Anaerobic

Can form spores

Commonly found in wounds and the GI tract.

37
Q

C.difficile pathogenicity

A

Toxins:
Increased fluid secretion into the gut which causes diarrhea.
Also increases sensitivity to infections.

Spore producing:
Makes treating and getting rid of the bacteria more difficult.

38
Q

Describe the structure of gram positive bacterial cell wall

A

Contains lipoteichoic acid anchored to the plasma membrane.

Thick peptidoglycan wall (20-80nm), which lipoteichoic acid passes through.

Lipid bilayer with integral proteins.

39
Q

Coagulase test

A

Test used to differentiate Staphylococcus aureus from other Staphylococcus.

This test is positive for Staph. aures as it produces the coagulase enzyme which clots blood.

40
Q

Catalase test

A

Tests if the bacteria possess catalase, which breaks down hydrogen peroxide into O2 and H2O.

Bubbling will be seen in the test if the bacteria is catalase-positive.

Streptococcus and Enterococcus are catalase-negative. This test is useful for differentiating Strep from Staph (which is catalase-positive)

41
Q

Oxidase test

A

Test for bacteria that tests for cytochrome oxidase c, an enzyme in bacteria’s electron transport chain.

Bacteria positive for this enzyme are aerobic as they use oxygen as their last electron acceptor. However negative result could also indicate aerobic bacteria.

Positive test- colour change into dark blue/ purple.

N.meningitidis is positive for this enzyme.
E. coli is negative for this enzyme.

Module 102: Infection and immunity (8 decks)

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