Professional Pathogens

Question 1

Infection

Answer 1

When an organism enters the body, increases in number and damages the host in the process

Question 2

A Pathogen

Answer 2

An organism which can evade the immune defences of the normal human host to cause infection. Pathogens almost always colonise before causing infection

Question 3

A Commensal

Answer 3

An organism which lives on us or in our gut but doesn’t cause infection

Question 4

Colonisation

Answer 4

When an organism lives on us but is not causing infection

Question 5

Symbiosis

Answer 5

Mutual benefit

Question 6

Parasite

Answer 6

Unequal benefit

Question 7

Professional pathogens (give example too)

Answer 7

Almost always cause disease. e.g. malaria, HIV, Neisseria meningitidis, Staphylococcus aureus, Streptococcus pneumoniae

Question 8

Opportunistic pathogens (give example too)

Answer 8

Only cause disease in immunocompromised patients. e.g. Staphylococcus epidermidis, candida albicans

Question 9

Why is there a spectrum between professional and opportunistic pathogens (a spectrum of pathogenicity)?

Answer 9

Because organisms vary in virulence

Question 10

How can low virulence organisms become pathogens?

Answer 10

If a patient is immunocompromised.

Question 11

Pathogenicity

Answer 11

Probability that an organism is causing disease in patient

Question 12

What does pathogenicity depend on?

Answer 12

Virulence, where sample is from (sterile or not), immune state of patient (steroids, diabetes, alcohol, T-cell deficiencies, neutropenia, burns, trauma, venous catheters), how sample was taken

Question 13

Brief profile of Staphylococcus aureus

Answer 13

Commensal of anterior nares, Gram positive cocci in clusters

Question 14

Name the virulence factors of S. aureus that allow it to be a good commensal and also a pathogen

Answer 14

Surface proteins (adhesins and protein A and coagulase), secreted proteins (toxins), capsule

Question 15

Staphylococcal capsule

Answer 15

Polysaccharide capsule, immunologically inert surface that allows S. aureus to evade immune response

Question 16

Protein A

Answer 16

Found on surface of S. aureus. Binds antibodies away from the antigen-complementary receptor, allowing immune evasion.

Question 17

Adhesins

Answer 17

Proteins on surface of S. aureus. Allow bacteria to stick to different tissues (via proteins) and also bind host proteins so that immune system cannot recognise bacteria

Question 18

Coagulase

Answer 18

Stimulates clotting, thus stopping white blood cells reaching site.

Question 19

Name the staphylococcal toxins secreted by S. aureus and describe their functions

Answer 19

Cytotoxins (forms pores in host cells, lysing them, including polymorphs), exofoliative toxins (cause skin to fall off, degrade connective tissue). Enterotoxins (In gut. Stimulate massive T cell activation and thus allows immune evasion. Ingestion of this toxin leads to vomiting).

Question 20

Why are there such massive immune responses to Gram negative bacteria?

Answer 20

Because of the lipopolysaccharide (endotoxins) on cell surface. Innate immune system very sensitive to these so strong immune responses.

Question 21

Which bacterium causes meningococcal septicaemia?

Answer 21

Neisseria meningitidis

Question 22

Which bacterium is responsible for the commonest form of pneumonia?

Answer 22

Streptococcus pneumoniae

Question 23

Sputum

Answer 23

A mixture of saliva and mucus coughed up from the respiratory tract, typically as a result of infection

Question 24

Mucosa

Answer 24

mucous membrane

Question 25

Spore forms of bacteria are resistant to:….. which makes them ideal for……

Answer 25

Drying out, alcohol, antibiotics (so can relapse after treatment). Ideal for survival in hospitals, allowing transfer between patients

Question 26

When do bacteria form spores?

Answer 26

When they are not dividing

Question 27

Give an example of a spore forming bacteria

Answer 27

Clostridium difficile

Question 28

Give two examples of Gram negative bacteria?

Answer 28

Neisseria meningitidis, Streptococcus pneumoniae

Question 29

Describe the effects on Clostridium difficile of taking antibiotics

Answer 29

C. difficile is resistant to many antibiotics. It will overgrow, producing toxins and diarrhoeal disease

Question 30

Virulence determinants and their importance, giving example

Answer 30

Secreted proteins, surface proteins, capsules etc. Important for identification of different species of bacteria and distinguishing between less and more virulent bacteria e.g distinguish virulent S. aureus from S. epidermis or distinguish S. aureus from less virulent strains. Less virulent will lack some of the virulence factors.