Micro-organisms in disease: infection Flashcards Preview

EMS - Mechanisms of disease > Micro-organisms in disease: infection > Flashcards

Flashcards in Micro-organisms in disease: infection Deck (23):
1

What are the requirements for pathogenicity?

Transmissibility
Establisment in or on a host
Harmful effects
Persistance

2

What is the chain of infection?

Reservoir -> Exit -> Transmission -> Entry -> Susceptible host -> Pathogenic organism

3

What is virulence and how does it differ from pathogenicity?

May be used interchangeably. Sometimes defined as the degree to which a organism is able to cause to disease ie relative description.

4

What are Koch's postulates?

- 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 newly inoculated animal
- Organism should be re-isolated from the experimentally infected animal

5

What are the possible routes of transmission?

Faecol-oral
Blood borne
Resp.
Direct contact - hand to hand, mucous membranes

6

What is infectivity?

The ability of a micro-organism to become established on/in a host. (microbial ligand/host cell surface repair)

7

Describe some common ligand-receptor interactions that occur between micro-organisms and host.

- E. coli P fimbriae binds to glycolipids on human uroepithelial cells - express specific adhesins
- S. pyogenes protein F binds to fibronectin - large multifunctional protein found in connective tissue on cells surfaces and in various body fluids
- Influenza haemagglutinin - resp. epithelial sialic acid receptors

8

What are virulence factors?

Components of micro-organisms that result in harmful effects.

9

What are potential virulence mechanisms?

Facilitation of adhesion

Toxic effects

Tissue damage

Interference with host defence mechanisms

Facilitation of invasion

Modulation of the host cytokine response

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

10

What is an endotoxin?

Component of the Gram neg bacterial cell wall. E. coli, N, meningitidis etc. Released from damaged/dead cells. Active component is LPS.

11

What are the effects of LPS on the body?

SIRS
- uncontrolled T-lymph response (cytokine release, ie TNF, IFN, IL-1)
- fever
- rigors
- hypotension
- tachycardia
- collapse
- cardiac/renal failure

DIC
- uncontrolled activation of clotting cascade
- depletion of clotting factors
- bleeding
- uncontrolled activation of complement

12

Why does limb loss occur in meningoccocal septicaemia?

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

13

What are exotoxins?

Proteins produced by living bacteria. Usually have quite specific effects on health.

14

What is the mode of action of botulinum toxin?

Cleaves SNARE proteins of secretory vesicles at NMJ - flaccid paralysis.

15

What is the mode of action of tetanus toxins?

Cleaves SNARE proteins of GABA secretory vesicles within inhibitory neurones - tetany.

16

What are the symptoms of botulism?

Diplopia, dysphagia, dysarthria, dry mouth, death from respiratory failure

17

What are the symptoms of tetanus?

Tetanospasm - produced on germination of spores
Opisthotonos - arched back
Sardonicus thingy

18

Give examples of other exotoxin-mediated infections.

Vibrio cholerae

Corynebacterium diptheriae - phage infected

C. diff - diarrhoea/colitis

E. coli O157 hemorrhagic colitis

Staph scolded skin syndrome - epidermolysin

Pertussis

Scarlet fever (Strep. pyogenes)

19

What is the key to treating a bacterial toxin-induced disease?

Given Abx to kill organism and anti-toxin.

20

What are the various S. pyogenes syndromes?

Strep throat

erysipelas

necrotizing fasciitis

scarlet fever (erythrogenic toxin - phage encoded).

21

Give examples of S.pyogenes virulence factors.

Hyaluronidase and streptokinase - break down connective tissue components, facilitate tissue invasion
C5a peptidase - inactivates complement

Streptolysins O and H - lyse red, white blood cells and platelets

Erytrogenic toxin (phage encoded) - scarlet fever
TSS toxin

22

How might bacteria inhibit phocytosis?

S.pyogenes - M-protein binds fibrinogen and masks bacterial surface - blocks complement and opsonisation

S.pneumoniae - polysaccaride capsule inhibits opsonisation

23

Give examples of intracellular pathogens.

Mycobacterium

Salmonella typhi

Listeria monocytogenes