Pathogens and the host: variously invasive pathogens

Question 1

How can virulence be measured?

Answer 1

From experiemental studies - lethal dose
Highly virulent pathogens show little difference in number of cells needed to kill 100% of population compared to 50% of population

Question 2

What is meant by lethal dose?

Answer 2

Lethal dose is the amount of agent that kills 50% of

Question 3

What is meant by attenuation?

Answer 3

the decrease or loss of virulence

Question 4

What is meant by invasiveness?

Answer 4

ability of pathogen to grow in host tissues at densities that inhibit host function - without producing toxin

Question 5

Toxicity is means of causing damage to host via production of toxin. True or false?

Answer 5

True

Question 6

Non-invasive pathogens involve viable bacteria but no penetration through epithelial layer. True or false?

Answer 6

True

Question 7

Is diptheria an invasive or non-invasive pathogen?

Answer 7

Non-invasin

Question 8

Diptheria bacteria are gram negative. True or false?

Answer 8

False - gram positive

Question 9

Non-invasive pathogens are localised at point of entry or mediated by exotoxins. True or false?

Answer 9

True

Question 10

Explain the pathogenisis of diptheria

Answer 10

Inhalation of aerosol - colonisation in throat
Produces single chained A-B toxin
Psuedomembrane forms in throat and A-B toxin inhibits elongation factor 2 in eukaryotic cells. This inhibits protein synthesis and therefore kills cell

Question 11

Is pertussis bacteria are gram positive. True or false?

Answer 11

False - gram negative

Question 12

DIptheria causes difficulty swallowing. True or false?

Answer 12

True

Question 13

Explain the pathogenisis of pertussis bacterium.

Answer 13

attached and replicate on ciliated upper respiratory tract mucosa
toxin production: pertussis exotoxin, trachael cytotoxin, invasive adenylate cyclase toxin
these cause loss of mucociliary clearance, violent coughing fits and secondary pneumonia

Question 14

How many toxins does the pertussis bacterium produce?

Answer 14

3

Question 15

Is pertussis bacterium invasive or non-invasive?

Answer 15

Non-invasive

Question 16

Is cholera bacterium gram positive or negative?

Answer 16

gram negative

Question 17

Explain the pathogenisis of cholera bacterium

Answer 17

Acute infection of GIT (small intestine)
production of cholera toxin - causes upregulation of adenylate cyclase and loss of fluid from GIT -> death through dehydration (unless prevented by rehydration therapy)

Question 18

What is meant by a partially-invasive pathogen?

Answer 18

Invade epithelial layer but don’t penetrate deeper tissue. They invade at primary site of infection only

Question 19

Are shigella bacteria gram positive or negative?

Answer 19

Negative

Question 20

Do shigella bacteria form spores?

Answer 20

No

Question 21

What is the clinical presentation of shigellosis?

Answer 21

Blood and puss in diarrhoea

Question 22

Explain the pathogenisis of shigella bacteria

Answer 22

attachment and invasion of ileum and colonic epithelia
produces A-B toxin
invasion is no deeper than lamina propria

Question 23

Invasive pathogens cause minimum damage at primary site of infection. True or false?

Answer 23

True

Question 24

How do invasive pathogens spread to lymphatics?

Answer 24

via lymph

Question 25

Is enteric fever caused by an invasive or non-invasive pathogen?

Answer 25

Invasive

Question 26

How is enteric fever transmitted?

Answer 26

Person-person or through consumption of contaminated food

Question 27

Enteric fever can be spread by animal reservoir. True or false?

Answer 27

False

Question 28

Explain the pathogenesis of enteric fever bacterium.

Answer 28

Bacterial induced uptake via M cells - travel through epithelia and cause systemic dissemination

Question 29

In food poisoning, is bacterial colonisation present?

Answer 29

No

Question 30

Food poisoning occurs on consumption of food contaminated with toxins of chemical or bacterial origin. True or false?

Answer 30

True

Question 31

Which bacteria causes botulism?

Answer 31

Clostridium botulinum

Question 32

Clostridium botulinum is gram positive. True or false?

Answer 32

True

Question 33

The botulinum bacteria is spore forming. True or false?

Answer 33

True

Question 34

Staphylococcus aureus can cause skin infections and food poisoning. True or false?

Answer 34

True

Question 35

How are symptoms produced by staph. aureus?

Answer 35

the bacteria produces an enterotoxin - toxin is ingested and interacts with gastric mucosa - symptoms

Question 36

Bacillus cereus doesn't form spores. True or false?

Answer 36

False

Question 37

What are the two disease forms of bacillus cereus?

Answer 37

emetic toxin - heat stable, short incubation | enterotoxin - heat labile, longer incubation