Micro-organisms in disease (11 and 12)

Question 1

Pathogenicity

Answer 1

Capacity of a micro-organism to cause an infection (transmissibility, establishment in/on a host, harmful effect, persistence)

Question 2

Virulence

Answer 2

(Same as pathogenicity) degree to which micro-organism is able to cause disease

Question 3

Koch’s postulates (1890)

Answer 3

• Organism should be present in disease but not in health.
• Organism should be isolated from the diseased animal and grown in pure culture
• Organism should cause the same disease in a newly inoculated animal.
• Organism should be re-isolated from the experimentally-infected animal.

Question 4

Infectivity

Answer 4

The ability of a micro-organism to become established on/in a host

Question 5

Examples of ligand-receptor interactions

Answer 5

E. coli P fibmriae: glycolipids on human uroepithelial cells

S.pyogenes protein-F: fibronectin

Influenza haemagglutinin: respiratory epithelial sciali acid receptors

Question 6

Virulence factors

Answer 6

Components of micro-organisms that result in harmful effects

Question 7

Virulence mechanisms

Answer 7

Facilitation of adhesion, toxic effect, tissue-damage, interference with host defence mechanism, facilitation of invasion, modulation of the host cytokine responses

Question 8

Virulence factors are sometimes referred to as

Answer 8

Adhesins, aggressin,s interferins, moduliun

Question 9

Virulence factors are encoded by

Answer 9

Virulence genes

Question 10

Endotoxin

Answer 10

Component of gram negative bacterial cell wall, released from damaged/deal cells, binds to a number of host cell receptors

Question 11

What is active component of an endotoxin?

Answer 11

Lipopolysaccharide (LPS)

Question 12

Examples of bacteria that have endotoxins

Answer 12

E.coli and other gram-negative bacilli, Neisseria meningitidis

Question 13

What is hosts response to an endotoxin?

Answer 13

Systemic inflammatory response syndrome (SIRS)

Question 14

What happens in SIRS?

Answer 14

Uncontrolled T-lymphocyte response, uncontrolled activation of the clotting cascade, uncontrolled activation of complement

Question 15

What happens in uncontrolled T-lymphocyte response?

Answer 15

• Cytokine release (TNF-a, y-interferon, IL-1)
• Fever, rigor, hypotension, tachycardia, collapse
• Cardiac and/or renal failure

Question 16

What happens in uncontrolled activation of the clotting cascade?

Answer 16

Disseminated intravascular coagulation (DIC), depletion of clotting factors, bleeding tendency

Question 17

What is Waterhouse-Friedrichsen syndrome?

Answer 17

Meningococcal infection > bilateral adrenal haemorrhage > adrenal failure (due to endotoxin Neisseria meningitidis)

Question 18

Exotoxins

Answer 18

Proteins produced by living bacteria, usually have quite specific effects on host

Question 19

What micro-organism causes Botulism?

Answer 19

Clostridium botulinum (obligate anaerobe)

Question 20

What causes Botulism?

Answer 20

Ingestion of pre-formed toxin (food) or infection of dirty wounds

Question 21

Where to Botulism toxin colonise?

Answer 21

GI (infants)

Question 22

Symptoms of Botulism

Answer 22

Diplopia, dysphagia, dysarthria, dry mouth, death, respiratory failure (no muscle contraction)

Question 23

What micro-organism causes Tetanus?

Answer 23

Clostridium tetani (obligate anaerobe)

Question 24

What causes Tetanus?

Answer 24

Infection of dirty wounds

Question 25

What toxin does Tetanus produce?

Answer 25

Tetanospasmin

Question 26

Tetanospasmin

Answer 26

Produced on germination of spores, binds to nerve synapses, inhibits release of inhibitory neurotransmitters in CNS

Question 27

How does death occur in tetanus?

Answer 27

Respiratory paralysis

Question 28

Opisthotonos

Answer 28

Spasm of muscles > backward arching of head, neck and spine

Question 29

Other exotoxin-mediated infections:

Answer 29

Cholera – Vibrio cholera

Diphtheria – Corynebacterium diphtheria

Clostridium difficile infection – diarrhoea/colitis

E. coli O157 haemorrhagic colitis (verotoxin)

Staphylococcal scalded skin syndrome – Staph. aureus

Whooping cough (pertussis) – Bordetella pertussis

Scarlet fever – Streptococcus progenies

Scalded-skin syndrome – Staph. aureus epidermolysin

Question 30

Streptococcus pyogenes

Answer 30

Promote connective tissue breakdown and invasion

Question 31

Streptococcus pyogenes syndromes

Answer 31

Streptococcal sore throat, Erysipelas, Necrotising fascilits (soft tissue infection), Scarlet fever

Question 32

Streptococcus pyogenes virulence factors

Answer 32

• Hyaluronidase and streptokinase (break down connective tissue)
• C5a peptidase (inactivates C5a)
• Streptolysins -O and -H (lyse RBC, WBC, platelets)
• Erythrogenic toxin (rash scarlet fever)
• Toxic shock syndrome toxin

Question 33

Necrotising fascilitis

Answer 33

Pain, black areas of inflammation/dead tissue, very sick, antibiotics insufficient, have to remove infected tissue (debriding)

Question 34

Which micro-organisms inhibit phagocytosis?

Answer 34

S. pyogenes and S. pneumoniae

Question 35

S. pyogenes inhibit phagocytosis by

Answer 35

M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation

Question 36

S. pneumoniae inhibit phagocytosis by

Answer 36

Polysaccharide capsule inhibits opsonisation and therefore phagocytosis

Question 37

Intracellular pathogens

Answer 37

Mycobacterium TB, Salmonella typhi, Listeria monocytogenes

Question 38

What is whole virus particle called?

Answer 38

A virion

Question 39

Virus life cycle

Answer 39

1. Adsorption (stick on cell)
2. Penetration (endocytosis)
3. Uncoating (genetic material released)
4. Synthesis
5. Assembly
6. Release (budding/cell burst)