How microbes cause disease

Question 1

Which degenerative enzymes are produced by bacteria which aid with the spread and growth of bacteria

Answer 1

Hyaluronidase-
breaks down hyaluronic acid

Collagenase- breaks down collagen network

proteases, nucleases, phospholipases-
depolymerise host proteins, nucleic acids, lipids

Question 2

List the two main mechanisms bacteria use to invade host cells

Answer 2

Triggered invasion and zippered invasion

Question 3

Describe the triggered invasion mechanism of bacteria. Give a bacteria which uses this mechanism

Answer 3

1. Bacteria inject virulence factors into host cytoplasm to activate uptake by cell
2. Bacteria bind weakly and use local cell protrusions which engulf the bacterium
3. salmonella and shingella

Question 4

Describe the zippered invasion mechanism of bacteria. Give a bacteria which uses this mechanism

Answer 4

1. Pathogen surface proteins bind with a high affinity to transmembrane receptors on the host cell
2. Pathogen is enveloped by the host cell membrane and taken in
3. listeria monocytogens and yersinia

Question 5

What is Septicaemia? What is Bacteraemia / viremia ?

Answer 5

pathogen in blood with evidence of host damage

Simply bacteria or virus in blood

Question 6

What are the main functions of the complement system?

Answer 6

1. opsonisation- C3b- pathogen clearance by phagocytosis
2. MAC- membrane attack complex (C5b)- direct lysis of pathogens
3. Enhancing inflammation (C5a): activation and recruitment of phagocytic cells by anaphylatoxins (C5a, C3a)

Question 7

What are the different ways phagocytes kill microorganisms?

Answer 7

Phagolysosome- after ingestion, phagosome is produced containg pathogen

This fuses with lysozyme which uses enzymes(defensins) to kill bacteria.

Nitric oxide
ROS- superoxidase, hydrogen peroxidase

Question 8

How do pathogens prevent phagocytosis?

Answer 8

1. Inhibit phagocyte mobilization-
   inhibit chemotaxins and chemoattractans and complement
2. Avoid ingestion- kill phagocytes,
   capsules protect from opsonisation
   use capsules which resemble host self molecules

Question 9

How do pathogens defend against phagolysozome?

Answer 9

1. they escape it and grow in cytoplasm
2. They inhibit the fusion of phagosome and lysosome
3. They survive inside it and inactive ROS, and replicate

Question 10

Which bacterias can produce a protease to destroy antibody A

Answer 10

H. influenzae
N. meningitidis
S. pneumoniae

Question 11

Name the 2 types of virulence toxins which can damage the host

Answer 11

Endotoxins- Released when bacteria die (lipopolysaccharide, peptidoglycan)

Exotoxins: released from live bacteria, 3 main types:
Cytolysins with cell membrane targets (pore forming)
A-B toxins: intracellular targets- act as enzymes

Toxins activate an immune responce (superantigens)

Question 12

How do Lipopolysaccharide damage the host?

Answer 12

lipid A is the toxic portion, activates complement and stimulates production of cytokines
(septic shock)

Question 13

Which disease are caused by A-B toxins? What was the toxins mode of action?

Answer 13

Diphtheria- Toxin inhibits protein synthesis in heart muscle
Tetanus- Toxin affects neuromuscular junctions (blocks GABA)
Botulism- Toxin affects neuromuscular junctions