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Flashcards in microorganisms in disease and infection Deck (40)
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1

define pathogenicity

the capacity of a micro-organism to cause an infection

2

what are the main characteristics which an organism must show to be pathogenic

transmissibility
establisment in or on a host
Harmful effects
Persistence

3

what are the stages in the chain of infection

pathogenic organism- in adequate numbers.
reservoir or source that allows the organism to survive and multiply.
mode of exit from the source
mode of transmission from the source to the host
Portal of entry through which the pathogen can enter the host
Suceptible host

4

define virulence

the degree to which a microorganism is able to cause disease.

5

what are the main routes of transmission for infection

faecal oral
blood borne
respiratory
direct contact- hand to hand to mucous membrane.

6

define LD50- Lethal dose

lethal dose- dose of organism which causes death in 50% of the exposed population.

7

define ID50- Infection dose

ID50-dose or organism which causes infection in 50% of the organism exposed.

8

how do pathogens colonise ( attachment to to what on surface of host cell)

Ligands in the organism binds to receptors on the surface of the host cell
Complementary ligand- receptor interaction.

9

define infectivity

The ability of a microorganism to become established in/on a host.

10

Examples of ligand receptor interactions

E. coli P fimbriae: glycolipids on human uroepithelial cells

S. pyogenes protein-F: fibronectin (Large multifunctional glycoprotein)

Influenza haemagglutinin: respiratory epithelial sialic acid receptors

11

what are the virulence mechanisms

adhesion, toxic affect, tissue damage, interference with host defence mechanisms, facilitation of invasion
modulation of host cytokine response.

12

what is a important toxin produced by the gram -ve bacterial cell wall and name infections where endotoxins are used

endotoxin
E.coli
Neisseria meningitidis.

13

In which layer of the gram -ve bacterial wall in endotoxin an active part of

active component of the liposaccaride membrane

14

when is an endotoxin released

released from damaged or dead cells.

15

what is a lipopolysaccharide made from

Lipid A, polysaccaride and a specific O antigen.

16

what is the host response to an endotoxin

uncontrollable T lymphocyte response- cytokine release, shock and cardiac and renal failure.
uncontrollable clotting cascade activation- DIC, depletion of clotting factors and a tendency to bleed.
uncontrollable complement activation.

17

what effects do the neisseria meningitidis endotoxin have on the host

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

18

Are exotoxin produced by living or dead bacteria

living

19

Are endotoxin produced by living or dead bacteria

dead

20

how does the Boutulism exotoxin work (where does it work)

affects the presynaptic membrane so that the neurotransmitter cannot be relased.

21

How does the preformed botulism toxin colonise the host.

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

22

what is the clinical presentation of botulism

diplopia, dysphagia, dysarthria, dry mouth, death, rigid paralysis (respiratory failure)

23

How does clostridium tetani colonise the host

infects wounds

24

what is the toxin in tetanus called

tetanospasim.

25

How does the tetanospasim (tetanous toxin work)

binds to nerve synapses
inhibited release of inhibitory neurotransmitter in the central nervous system.

26

what are the main clinical presentations of tetanus

Jaw spasm
rigid paralysis
opisthotonos (body thrown into shapes which depends on muscle strength)
death caused by respiratory paralysis

27

what is the treatment for tetanus

metronidazole and tetanus antitoxin.

28

what effect do the strep pyogenes virulence factors have

promote connective tissue breakdown and invasion.

29

what infections can strep pyogenes cause

streptococcal sore throat
Erysipelas- skin infection
Necrotizing fascilitis.
Scarlet fever- streptococcus (sore throat caused by erthyrogenin toxin.)

30

what is the function of Hyaluronidase and streptokinase virulence factor of S pyogenes

Break down connective tissue components – facilitate tissue invasion