Infectious Agents

Question 1

How are microbes visualised?

Answer 1

Bacteria, fungi, protozoa, and helminths
- can be seen using light microscope (x400 to x 1000)

Viruses seen via EM x40,000

Question 2

How does bacterial growth occur?

Answer 2

Via binary fission with each doubling taking 20-30 mins at optimum of 35-37 ℃

Question 3

Describe the structure of a virus

Answer 3

20-300um
DNA/RNA genome
Linear, segmented, single or dsGenomes of varying sizes 9kb - 300kb
Have nucleocapsid (protein core)
No cytoplasm
(non)Enveloped
May have host component on viral membrane

Question 4

What is the Linnean classification system?

Answer 4

Domain 
Kingdom 
Phylum 
Class 
Order 
Family 
Genus 
Species

Question 5

What is required for bacterial growth?

Answer 5

• Carbon, water, nitrogen
• nutrients & minerals
• correct osmotic pressure
• correct pH
• correct Temperature
• correct atmosphere

Question 6

Describe the key features of protozoa

Answer 6

• single cells
• 5-300 um
• single / multiple nuclei
• trophozites, cysts, and othe rmorphocytes have complex
  life cycles
• Haploid DNA
• Morphology varies throughout life cycle
• can have flagella

Question 7

How are different virus’ classified?

Answer 7

Viruses can be classified based on their protein nucleocapsid structure

• helical
• cubic
• complex arrangement

Question 8

Describe the Ebola virus

Answer 8

Enveloped RNA virus with a very complex nucleocapsid part of the filoviridae family

Question 9

What criteria is used to classify pathogenic organism?

Answer 9

• Structural, functional and metabolic observations

- Molecule and genetic / genome analysis

Question 10

What are helminths?

Answer 10

Multicellular parasitic worms

Question 11

Describe the key features of Bacteria

Answer 11

• 1/1000th of a mm
• 0.5 - 3um
• Prokaryotic
• Haploid DNA
• Circular genome
• no nucleus
• no mitochondria
• undergoes binary fission
• usually has rigid cell wall outside cytoplasmic membrane

Question 12

What is the significance of pathogenic organism classification?

Answer 12

Identification is essential to understand the (micro)biology, evolution & phylogenetics, pathogenesis of infectious diseases, life cycles, diagnosis, effective treatment and public health control of infectious diseases

Question 13

What are parasites?

Answer 13

Organisms that live in an organism of another species (host) and benefits by deriving nutrients at the other’s expense

Question 14

What is the difference in the movement of motile and non motile bacteria?

Answer 14

Motile bacteria with flagella move rapidly

Non motile bacteria move ‘on the spot’

Question 15

Compare and contrast prokaryotes and eukaryotes

Answer 15

Prokaryotes e.g. bacteria

• No nucleus
• no mitochondria
• mainly circular DNA

Eukaryotes

• chromosomes
• nucleus
• membrane bound organelles

Question 16

Describe structural features of helminths

Answer 16

• Have different morphologies and sizes at different
  stages of their life cycles
• Can be microscopic or visible to the eye

Question 17

What technique is used to distinguish between bacterial species?

Answer 17

Gram staining bacteria
stains include:
- iodine, alcohol, safranin

Question 18

Where do virus’ replicate?

Answer 18

Virus’ are obligate intracellular organisms so can only replicate inside host cells

Question 19

What are the biological characteristics of the 4 microbes?

Answer 19

All organisms are cells except viruses - don’t have membranes
Cell life cycles, cellular and genome organisation
Parasites are multi-cellular

Question 20

Name 3 examples of Fungi / their infections caused

Answer 20

Superficial mucosa
- skin, nail, hair & mucosal membranes (dermatophytes) or
thrush

Cutaneous - Tanea (ringworm)

Systemic muycoses e.g. histoplasmosis

Question 21

What are the 3 groups of helminths?

Answer 21

Cestode - tapeworms e.g. taenia, saginata (beef
tapeworm)

Trematode - flatworms or flukes including: schistoma
haematobium
-> cause of bilharzia / schistosomiasis

Nematodes - roundworms e.g. Ascaris lumbricoides

Question 22

Compare the 4 types of microbes with each other

Answer 22

Parasites are more complex than viruses
Viruses are tiny in comparison to bacteria and protozoa
Bacteria are x10 or x100 smaller compared to animal / plant cells
Light microscopes used to see bacteria
Electron microscope used to see viruses

Question 23

Outline the life cycle of a virus

Answer 23

1. Attachment - virus attaches to target cell
2. Penetration - cell engulfs virus via endocytosis
3. Uncoating - viral contents released
4. Biosynthesis - viral RNA enters nucleus, replicated by
   viral RNA Pol
5. Assembly - New phage particles made and released
   into extracellular fluid - cell continues new virus
   production

Question 24

Describe the structure of the Influenza Virus

Answer 24

Influenza virus is an enveloped virus with surface haemaglutinin

Question 25

What is fungi classification based on?

Answer 25

Fungi classification is complex and based on morphology, reproduction mode (Sexual/asexual) and disease caused
It’s easier to consider fungi by type of infection

Question 26

What are the 4 major microbe types?

Answer 26

Viruses
Bacteria
Fungi
Parasites

Question 27

Describe the structural features of fungi

Answer 27

• over 2um
• eukaryotic
• can be single or multi-cellular
• Haploid or diploid
• single or multiple nuclei
• rigid chitinous cell wall

Question 28

Describe the features of Adenovirus

Answer 28

Adenovirus is an example of non-enveloped DNA virus usually associated with conjunctivitis

Question 29

Give examples of the different structures of fungi

Answer 29

Yeast
spheroid single cells budding and dividing

Filamentous forms / moulds
hyphae
multi-nucleating branching hyphae form mycelium

Question 30

Describe anaerobic bacteria growth and visualisation

Answer 30

anaerobic bacteria only grow in absence of O2

Gram +ve, rod like spores forming

Question 31

How are microbes classified?

Answer 31

Based on:

• size
• biological complexity
• life cycles
• prokaryotes / eukaryotes
• haploid / diploid
• genomes and genetics