Lect 11 & 12 - Micro-organisms in disease - Fri 16th Oct

Question 1

whats Pathogenicity

Answer 1

The capacity of a micro-organism to cause an infection

Question 2

what is needed to increase Pathogenicity

Answer 2

Transmissibility
Establishment in or on a host
Harmful effect(s)
Persistence

Question 3

what are the steps in the chain of infection?

Answer 3

entry
susceptible host
pathogenic organism
reservoir
exit
transmission
back to entry.

Question 4

what is virulence?

Answer 4

May be used interchangably to describe pathogenicity

Virulence sometimes defined as the degree to which a micro-organism is able to cause disease.

Question 5

what is Infectivity?

Answer 5

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

Question 6

what do pathogens use to increase infectivity?

Answer 6

Ligand-receptor interactions -

for example fimbriae used by E. coli to attach to glycolipids on human uroepithelial cells

Question 7

give examples of Virulence mechanisms

Answer 7

Facilitation of adhesion
Toxic effect(s)
Tissue-damage
Interference with host defence mechanisms
Facilitation of invasion
Modulation of the host cytokine responses

Sometimes referred to as adhesins, aggressins, interferins, modulins etc.

Question 8

what are virulence genes?

Answer 8

genes that encode for Virulence factors

Question 9

what is an Endotoxin?

Answer 9

Released from damaged/dead cells
Active component is lipopolysaccharide - LPS
Binds to a number of host cell receptors
Induces a range of uncontrolled host responses

Question 10

what type of bacteria have endotoxins as part of their cell wall?

Answer 10

Gram-negative

Question 11

what happens in the host when endotoxins are released?

Answer 11

Systemic inflammatory response syndrome (SIRS)

Question 12

what are the components of SIRS?

Answer 12

Uncontrolled T-lymphocyte response

Uncontrolled activation of the clotting cascade

Uncontrolled activation of complement

Question 13

What does Uncontrolled T-lymphocyte response cause?

Answer 13

Cytokine release: TNF-α, γ-interferon, interleukin-1

Fever, rigors, hypotension, tachycardia, collapse

Cardiac and/or renal failure

Question 14

what does Uncontrolled activation of the clotting cascade cause?

Answer 14

Disseminated intravascular coagulation (DIC):

Depletion of clotting factors

Bleeding tendency

Question 15

give examples of gram negative bacteria which tend to give off endotoxins

Answer 15

E. coli and other Gram-negative bacilli

Neisseria meningitidis

Question 16

describe symptoms of Neisseria meningitidis infection

Answer 16

Endotoxin-mediated increase in vascular permeability causes loss of protein, fluid and plasma into the tissues, with pathological compensatory vasoconstriction

Question 17

what are exotoxins?

Answer 17

Proteins produced by living bacteria

Usually have quite specific effect(s) on host

Question 18

what is Botulism caused by

Answer 18

Clostridium botulinum (obligate anaerobe)

Ingestion of pre-formed toxin
(Contaminated food)
Infection of dirty wounds
(May be trivial wounds)
Gastrointestinal colonisation

Question 19

what does Botulinum toxin do?

Answer 19

prevents muscle contraction

Question 20

whats is the clinical presentation of botulism?

Answer 20

Diplopia (double vision)
Dysphagia (cant swallow)
Dysarthria (cant talk)
Dry mouth
Death
Respiratory failure

Question 21

what causes Tetanus?

Answer 21

Clostridium tetani
Infection of dirty wounds
May be trivial wounds

Question 22

what kills people with tetanus?

Answer 22

respiratory paralysis

Question 23

how does the tetanus toxin interact with the body?

Answer 23

Binds to nerve synapses

Inhibits release of inhibitory neurotransmitters (e.g. gamma-amino butyric acid) in the central nervous system

Question 24

what causes cholera?

Answer 24

Vibrio cholerae

Question 25

what causes Diphtheria

Answer 25

Corynebacterium diphtheriae

Question 26

what causes haemorrhagic colitis ?

Answer 26

E. coli O157 - an endotoxin

Question 27

what causes Staphylococcal scalded skin syndrome

Answer 27

Staph. aureus

Question 28

what casues Whooping cough (pertussis)

Answer 28

Bordetella pertussis

Question 29

what causes Scarlet fever

Answer 29

Streptococcus pyogenes

Question 30

what causes Scalded-skin syndrome

Answer 30

Staph. aureus epidermolysin

Question 31

give a list of diseases caused by exotoxins

Answer 31

Botulism
Tetanus
Cholera
Diphtheria
Clostridium difficile
haemorrhagic colitis
Staphylococcal scalded skin syndrome 
Whooping cough (pertussis)
Scarlet fever

Question 32

what does Streptococcus pyogenes cause? (in addition to scarlet fever)

Answer 32

has virulence factors that promote connective tissue breakdown ands invasion

Streptococcal sore throat
Erysipelas
Necrotizing fasciitis
Scarlet fever

Question 33

what virulence factors does Streptococcus pyogenes have?

Answer 33

Hyaluronidase and streptokinase
C5a peptidase
Streptolysins -O and –H
Erythrogenic toxin (phage-encoded)
Toxic shock syndrome toxin

Question 34

what do Hyaluronidase and streptokinase do?

Answer 34

Break down connective tissue components – facilitate tissue invasion

Question 35

what does C5a peptidase

do?

Answer 35

inactivates complement component C5a

Question 36

what do Streptolysins -O and –H do?

Answer 36

Lyse red and white blood cells and platelets

Question 37

what does Erythrogenic toxin do?

Answer 37

Causes the rash of scarlet fever

Question 38

how does S. pyogenes avoid phagocytosis

Answer 38

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