Bacteria and Disease

Question 1

What is pathogenicity?

Answer 1

The ability of a pathogen to inflict damage on a host

Question 2

What is virulence?

Answer 2

The relative ability of a pathogen to cause disease

Question 3

What can virulence be estimated from?

Answer 3

Experimental studies of the LD50 (lethal dose 50) - the amount of an agent that kills 50% of the animals in a test group

Question 4

What are virulence factors and what are some of their roles?

Answer 4

Bacteria-associated molecules which enable the bacterium to damage the host and cause disease
e.g adherence to host cells, invasiveness, nutrient acquisition, immune evasion, toxins, superantigens, antibiotic resistance

Question 5

Infection of pathogen process

Answer 5

1. Exposure - doesnt alwys result in infection
2. Adherence to skin or mucosa - adhesins like glycoproteins or lipoproteins extend from bacterial surface
3. Invasion through epithelium
4. Multiplication

Question 6

Why is adherence necessary?

Answer 6

To avoid innate host defense mechanisms e.g peristalsis in gut, flushing action of mucus, saliva

Question 7

What important functions in bacterial pathogenicity do polymer coats play?

Answer 7

1) Contain specific receptors to enable adhesion to host cells
2) Protect bacteria from ingestion by wbcs

Question 8

What is colonisation?

Answer 8

The growth of microorganisms after theyve gained access to host tissues
Bacteria typically colonise host tissues which are in contact w external environment

Question 9

What is invasion mediated by?

Answer 9

A range of molecules called invasins

Question 10

What helps a pathogen break down host tissues in invasion?

Answer 10

Enzymes e.g hyaluronidase and collagenase

Question 11

What is the function of hyaluronidase in invasion?

Answer 11

Breaks down hyaluronic acid which holds cells together, enabling bacteria to invade deeper into tissues

Question 12

What is the function of collagenase in invasion?

Answer 12

Breaks down collagen which surrounds endothelial cells, allowing bacteria to enter the bloodstream

Question 13

What is bacteraemia?

Answer 13

the presence of bacteria in the bloodstream

Question 14

What is septicaemia?

Answer 14

Bloodborne systemic infection - leads to massive inflammation . septic shock and death

Question 15

What do bacteria produce to speed up the formation of a fibrin clot from fibrinogen to hide from immune cells?

Answer 15

Coagulase

Question 16

What does the bacteria produce to dissolve the clot and be released into the bloodstream?

Answer 16

Kinase e.g staphylokinase

Question 17

What are the benefits of bacteria surviving intracellularly inside host cells?

Answer 17

1) Protects them from parts of immune response
2) Enables them to avoid clearance by shear stress/ secretions
3) Gives them access to a wide range of nutrients

Question 18

Opportunistic VS Obligate intracellular pathogens

Answer 18

Opportunistic - E.coli
Obligate - Chlamydia

Question 19

How do bacteria get inside host cells?

Answer 19

1) Engulfed by an immune cell (phagocyte)
2) Force a non-phagocyte e.g epithelial/endothelial cell to engulf them

Question 20

How do bacteria cells force a non-phagocytic cell to engulf them?

Answer 20

Bacteria cause cell signalling cascade within host cell which leads to actin reorganisation and engulfment

Question 21

How does Salmonella force its way into human cells?

Answer 21

-Uses a needle like structure to inject proteins into host cell
-These proteins cause reorganisation of the actin cytoskeleton leading to an uptake of bacterium
-Within host (human) cell, Salmonella is enclosed inside a vacuole where it survives and proliferates

Question 22

What nutrient is required by most pathogenic bacteria and how do they acquire this nutrient?

Answer 22

Iron is required for most pathogenic bacteria
Siderophores are proteins secreted by pathogens that bind to iron more tightly than host cells

Question 23

What is toxicity?

Answer 23

The ability of an organism to cause disease by means of a toxin that inhibits host cell function or kills host cells

Question 24

Where are endotoxins found and what is Lipid A responsible for?

Answer 24

-Only found in gram neg bacteria - LPS
- Lipid A is responsible for toxic properties - gut microbiota have non toxic LPS

Question 25

What is a pyrogen?

Answer 25

LPS is a pyrogen
-Triggers the immune systems inflammatory response - causes fever, septic shock, death

Question 26

How are endotoxins detected?

Answer 26

By LAL assay - Limulus amebocyte lysate assay
Blood of horse shoe crabs contain amebocytes which lyse in the presence of endotoxin creating a blood clot

Question 27

What are endotoxins made from?

Answer 27

Proteins

Question 28

What are AB-Type Exotoxins made up of and what are examples?

Answer 28

AB toxins are made up of an Active (A) domain and a binding (B) domain
E.g : diphtheria toxin, tetanus toxin, botulinum toxin, cholera toxin

Question 29

What is Diphtheria Exotoxin produced by and what is its function?

Answer 29

Produced by Corynebacterium diphtheriae

Blocks protein synthesis
- The A domain adds an ADP-ribosyl group to EF-TU, which prevents its func in translation - causes cell death

Question 30

What is Botulinum toxin and what produces it?

Answer 30

A neurological exotoxin- affects the NS

Produced by Clostridium botulinum

-One of most potent biological toxins known

Question 31

What is tetanus toxin, what produces it and where does it affect?

Answer 31

-Neurological exotoxin
-Produced by Clostridium tetani
-Spores live in soil and enter person through a wound
-Toxin is transported to CNS causing involuntary contraction of skeletal muscles

Question 32

What is Cholera toxin produced by, what kind of exotoxin is it and what does it cause?

Answer 32

-Produced by Vibrio cholerae
-Cholera is an enterotoxin - an exotoxin that affects the small intestine
-Causes massive secretion of fluid into intestinal lumen - vomiting and diarrhea

Question 33

What are cytolytic toxins?

Answer 33

Toxins that degrade cytoplasmic membrane integrity causing cell lysis and death

Question 34

What are haemolysins?

Answer 34

Toxins that lyse RBCs
-Staphylococcal alpha-toxin kills nucleated cells and lyses RBCs

Question 35

What toxin destroys neutrophils and macrophages?

Answer 35

Leucocidin

Question 36

What are Superantigen Exotoxins?

Answer 36

-cause a non-specific overstimulation of immune cells
-excessive production of cytokines = cytokine storm
-causes a strong inflammatory response
-can lead to high fevers, low blood pressure, multi organ failure, shock and death
-generally due to a localized infection but w systemic effects
-e.g is toxic shock syndrome toxin produced by staphylococcus aureus

Question 37

What is attenuation?

Answer 37

The process of pathogens losing their virulence
-attenuated strands can be used as vaccines

Question 38

Example infection - What is dental caries produced by?

Answer 38

Streptococcus mutans - part of oral microbiota

Question 39

Example infection - Dental caries - 1) Adherence and Colonisation

Answer 39

1. attachment of single cells
2. growth into microcolonies
3. metabolises sugar into polysaccharides
   -biofilm known as PLAQUE

Question 40

Example infection - dental caries - 2) Invasion and Tissue damage

Answer 40

Lactic acid bacteria
Covert sugar into lactic acid
-damages tooth surface
-bacteria invade deeper into tooth
-abscess
-reach blood stream - endocarditis