Pathogens

Question 1

Pathogen

Answer 1

Microbe that causes disease

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

Question 2

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

Answer 2

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

Question 3

Virulence

Answer 3

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

Question 4

Pathogenicity

Answer 4

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.

Question 5

Opportunistic pathogens

Answer 5

Only causes disease when in immunocompromised patients.

Low virulence organisms become pathogens.

Question 6

Infection

Answer 6

When an organism:

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

Invasion –> Replication –> Damage

Question 7

Commensal

Answer 7

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

Question 8

The main features of the immune system.

Answer 8

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)

Question 9

Strain of bacteria

Answer 9

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

Question 10

Different shapes of bacteria

Answer 10

Coccus/ Cocci: Round

Bacilli/ Bacillus: Long

Spiral/ branched

Vibrio (comma shape)

Question 11

Gram positive baceteria

Answer 11

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

Question 12

Gram negative bacteria

Answer 12

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.

Question 13

Describe the Gram staining technique.

Answer 13

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

Question 14

Bacterias that cannot be tested through Gram staining

Answer 14

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

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

Question 15

Lipopolysaccharide

Answer 15

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.

Question 16

Peptidoglycan

Answer 16

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.

Question 17

Patterns of bacterial growth

Answer 17

Clusters: ‘Staph’ bacteria.

Chains: ‘Strep’ bacteria.

Question 18

Peptidoglycan synthesis in bacteria

Answer 18

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.

Question 19

Mycobacteria

Answer 19

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

Question 20

Capsule

Answer 20

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.

Question 21

Transposons

Answer 21

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

Question 22

Spores

Answer 22

Seed-like projections that form from some bacteria:

The spores are non-replicating and dormant.

Resistant to :
Drying
Temperature
Disinfection 
Digestion

Question 23

When does gene regulation occur during bacterial growth?

Answer 23

Lag and stationary phase

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

Question 24

Ribosome in bacteria

Answer 24

70S

Subunits 50S and 30S.

Question 25

Staphylococcus aureus

Answer 25

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.

Question 26

Virulence of S.aureus | SSC

Answer 26

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.

Question 27

Toxins of S.aureus. CEE

Answer 27

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

Question 28

Adhesins of S.aureus

Answer 28

Protein A Collagen binding protein Fibronectin binding protein Elastin binding protein.

Question 29

S. aureus skin infections

Answer 29

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

Question 30

S.aureus line sepsis

Answer 30

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

Question 31

S.aureus infections

Answer 31

Vascular line related infections Epidermal infections Bacteremia Surgical site infections

Question 32

Toll like receptors

Answer 32

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

Question 33

Meningococcal septicaemia

Answer 33

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).

Question 34

Meningococcal pathogenicity

Answer 34

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

Question 35

Staphylococcus pneumoniae virulence

Answer 35

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.

Question 36

Clostridium difficile

Answer 36

Gram positive bacillus bacteria: Anaerobic Can form spores Commonly found in wounds and the GI tract.

Question 37

C.difficile pathogenicity

Answer 37

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.

Question 38

Describe the structure of gram positive bacterial cell wall

Answer 38

Contains lipoteichoic acid anchored to the plasma membrane. Thick peptidoglycan wall (20-80nm), which lipoteichoic acid passes through. Lipid bilayer with integral proteins.

Question 39

Coagulase test

Answer 39

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.

Question 40

Catalase test

Answer 40

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)

Question 41

Oxidase test

Answer 41

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.