Bacteria & Disease

Question 1

Pathogenicity

Answer 1

The ability of a pathogen to inflict damage on host

Question 2

Infection

Answer 2

Microorganism (not a member of local microbiota) is established & growing in host

Question 3

Pathogen

Answer 3

Organism that causes disease or tissue damage in a host

Question 4

Virulence

Answer 4

The relative ability of a pathogen to cause disease

Question 5

How can virulence be estimated

Answer 5

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

Question 6

Roles of virulence factors (7)

Answer 6

• adherence to host cell
• invasiveness
• nutrient acquisition from host
• immune evasion - inhibition of phagocytosis
• toxins
• superantigens
• antibiotic resistance

Question 7

Steps of infection process

Answer 7

1. Exposure to pathogens
2. Adherence to skin or mucosa
3. Invasion through epithelium
4. Multiplication - growth & production of virulence factors and toxins

Question 8

Compromised physical defences examples

Answer 8

• Broken skin
• Injections/surgery
• In-dwelling medical devices

Question 9

Swimming motility in bacteria is controlled by what

Answer 9

Flagella

Question 10

Why is adherance of the bacteria necessary

Answer 10

To avoid innate host defense mechanisms - peristalsis in gut, flushing action of mucous/saliva/urine

Question 11

What are the receptors on bacteria called

Answer 11

Adhesins
They extend from bacterial surface.

Question 12

What are adhesins often

Answer 12

• Glycoproteins
• Lipoproteins

Question 13

What 2 functions do glycocalyx play in bacterial pathogenicity

Answer 13

1. They contain specific receptors to enable adhesion to host cells
2. Protect bacteria from ingestion by wbcs

Question 14

Fimbriae & Pili functions

Answer 14

• Gene transfer by conjugation
• Attachment to human tissue
• Motility

Question 15

Colonisation

Answer 15

The growth of microorganisms after they’ve gained access to host tissues

Question 16

Why do bacteria show tissue specificity

Answer 16

Different bacteria have different nutritional & environmental needs

Question 17

Which bact adapted to survival in gastrointestinal tract

Answer 17

Salmonella & Shigella
Good at surviving in low pH

Question 18

Invasion

Answer 18

Penetration of host cells & tissues beyond skin & mucous surfaces

Question 19

What is invasion mediated by

Answer 19

Molecules called invasins

Question 20

Example of enzymes as virulence factors (2)

Answer 20

1. Hyaluronidase breaks down hyaluronic acid which holds cells together, enabling bacteria to invade deeper tissues
2. Collagenase breaks down collagen which surrounds endothelial cells, allows bacteria enter bloodstream

Question 21

Bacteraemia

Answer 21

The presence of bacteria in the bloodstream

Question 22

Septicaemia

Answer 22

Bloodborne systemic infection

Question 23

What protects bacteria from phagocytosis by immune cells in the bloodstream

Answer 23

Formation of a fibrin clot protects bacteria from phagocytosis by immune cells

Question 24

Benefit to bacteria of travelling inside host cells

Answer 24

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

Question 25

Example of opportunistic intracellular pathogen

Answer 25

E. coli

Question 26

Example of obligate (needs oxygen) intracellular pathogen

Answer 26

Chlamydia

Question 27

How do bacteria get inside host cells (2)

Answer 27

1. Engulfed by immune cell (phagocyte) 2. Force a non phagocyte (epithelial/endothelial cell) to engulf it

Question 28

How does Salmonella force its way into human cells

Answer 28

* Needle like structure injects proteins into host cell * Causes reorganisation of actin cytoskeleton leading to uptake of bacterium * Salmonella enclosed in vacuole - survives & proliferates

Question 29

What nutrient is required for most bacteria

Answer 29

Iron

Question 30

How do bacteria get iron

Answer 30

* Secrete proteins called siderophores that bind iron more tightly than host cells * (If cell loses too much iron it can die, this on a wide scale causes anaemia)

Question 31

Toxicity

Answer 31

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

Question 32

What kind of bacteria have endotoxins

Answer 32

* Gram neg bacteria * Lipid A portion of LPS responsible for toxic properties * Only pathogenic bacteria have toxic LPS

Question 33

What assay detects endotoxins

Answer 33

Limulus amebocyte lysate (LAL) assay. Amebocytes lyse in presence of endotoxin, producing a clot.

Question 34

What are AB exotoxins composed of

Answer 34

* An active (A) domain * Binding (B) domain

Question 35

4 examples of AB exotoxins

Answer 35

1. Diphtheria toxin 2. Tetanus toxin 3. Botulinum toxin 4. Cholera toxin

Question 36

What is happening to acetylcholine in botulism vs in tetanus

Answer 36

* Acetylcholine inhibited in botulism, results in flaccid paralysis * Acetylcholine constantly being released in tetanus, muscle constantly contracts resulting in spastic paralysis

Question 37

Enterotoxin

Answer 37

An exotoxin whose activity affects small intestine

Question 38

What does cholera toxin cause

Answer 38

Massive secretion of fluid into intestinal lumen, resulting in vomiting & diarrhoea

Question 39

What do cytolytic toxins do

Answer 39

degrade cytoplasmic membrane integrity, causing cell lysis & death

Question 40

What do superantigen exotoxins do

Answer 40

* Cause a non specific overstimulation of immune cells * Strong inflammatory response, can lead to high fevers, low bp, multi organ failure, shock, death

Question 41

What is the process where pathogens lose their virulence called

Answer 41

Attenuation (Due to mutation)

Question 42

What can attenuated strains be used as

Answer 42

Vaccines e.g: TB vaccine

Question 43

Endotoxin vs exotoxin: LD50

Answer 43

* Endotoxin have a high LD50 * Exotoxins have low LD50 (so only a small amount is needed to see effects - more dangerous)