Biological Agents as Causes of Disease

Question 1

Define pathogen

Answer 1

A disease-causing organism

Question 2

Types of pathogens

Answer 2

• obligate
• facultative
• opportunistic

Question 3

What is an obligate pathogen?

Answer 3

A pathogen that only survives in its host

Question 4

What is a facultative pathogen?

Answer 4

A pathogen that is present in the environment, waiting for a host

Question 5

What is an opportunistic pathogen?

Answer 5

A pathogen that is normally benign but causes disease in a compromised host

Question 6

Why do pathogens make us sick?

Answer 6

• The symptoms of the disease usually help spread the pathogen
• Side effect of pathogen killing cells in order to replicate

Question 7

Examples of diseases that bacteria cause

Answer 7

Gonorrhoea, syphilis, food poisoning, cholera

Question 8

Examples of diseases that eukaryotes cause

Answer 8

Athlete’s foot, malaria, thrush

Question 9

Examples of disease that viruses cause

Answer 9

AIDS, small pox, common cold

Question 10

What are virulence genes?

Answer 10

The few genes that are different between two closely related species. Can be pathogenic/harmless

Question 11

What do fungi often show in their life cycle?

Answer 11

Dimorphism

Question 12

Using a example, describe dimorphism in a fungi

Answer 12

Candida albicans
The soil form grows as a mould - tubular cells
but in a warm body, switches to the yeast morphology
After macrophages engulf them, the fungi grows “germ tube”
This projection pierces and kills the macrophage

Question 13

Example of disease associated with protozoa

Answer 13

Malaria

Question 14

What is used as a vector in malaria?

Answer 14

Mosquitos

Question 15

Barriers to pathogens

Answer 15

Bacteria, Flora, Fungi which densely populate most epithelium

Question 16

What are epithelial cells held together by and why?

Answer 16

Tight junctions so that pathogens cannot squeeze between cells

Question 17

Often epithelia secrete…

Answer 17

…mucous

Question 18

What do white blood cells do in terms of epithelia?

Answer 18

Quickly recognise breaks in the epithelia

Question 19

Breaks in the epithelia are quickly recognised by…

Answer 19

White blood cells

Question 20

How do some bacteria anchor themselves to epithelia?

Answer 20

Some bacteria have P pili and use adhesins to anchor themselves to the epithelia

Question 21

Why do pathogens breach the cell membrane?

Answer 21

To inject toxins or to replicate inside the cell

Question 22

Why might a pathogen want to inject toxins into a host cell?

Answer 22

To kill the cell in order to provide itself with nutrients

Killing WBCs help in evading the immune system

Question 23

3 main methods pathogens use to evade the immune system

Answer 23

1. Type III secretion system
2. Assemble a pedestal
3. Hide

Question 24

Many bacteria have type…

Answer 24

…III secretion systems that act like a syringe

Question 25

___ assembles an ____ to anchor them and overcome barriers

Answer 25

E.coli. Actin pedestal

Question 26

Bacteria ___ to enter cells

Answer 26

Hide

Question 27

What bacteria causes Legionairre’s disease?

Answer 27

Legionella Pneumophila

Question 28

What does legionella pneumophila normally infect?

Answer 28

Amoeba

Question 29

If inhaled, legionella pneumophila is phagocytosed by macrophages. Which cells do they replicate inside?

Answer 29

Macrophages, unlike most bacteria

Question 30

Two other ways bacteria invade non-phagocytic cells

Answer 30

• attaching to cell receptors like velcro

- forcing the cell to rearrange actin structures

Question 31

Listeria entering the cell

Answer 31

L. monocytogenes secrete hemolysin which breaks down the membranes of lysosomes
Effects the stopped by PEST amino acid sequence which tags for destruction
L. monocytogenes then replicate inside the cell

Question 32

Listeria entering neighbouring cells

Answer 32

After replicating inside the first cell, they assemble actin tails that push them into neighbouring cells. Uses ActA

Question 33

What is ActA?

Answer 33

A bacterial protein that is localised to the tail end and nucleates actin polymerisation at that end of the cell. Listeria uses to enter neighbouring cells

Question 34

How do antibiotics stop bacterial growth?

Answer 34

By stopping cell process.