Session 1 ILOs - Introduction to infection and microbes

Question 1

Definition of infection

Answer 1

Infection is the invasion and multiplication of micro-organisms in a host’s tissues that are not normally present (may be symptomatic or asymptomatic)

Question 2

Explain the 2 types of transmission: Horizontal (diff types) and vertical

Answer 2

Horizontal:

• Contact (direct, indirect or vectors)
• Inhalation (droplets or aerosols)
• Ingestion (faecal-oral)

Vertical
- From mother to child (before or during birth)

Question 3

Explain how we know patients have an infection (including the meaning of the 2 types of investigations)

Answer 3

1. History
   - Symptoms
   - Potential exposure
2. Examination
   - Organ dysfunctions
3. Investigations
   - Specific e.g. swabs etc. for bacteriology/virology - tries to identify the causative organism
   - Supportive e.g. CRP, FBCs etc - tells you if the patient has an infection, but can’t give you a name

Question 4

Name the 4 main categories of micro-organisms (smallest first)

Answer 4

• Viruses
• Bacteria
• Fungi
• Parasites

Question 5

Name 3 key features of a model virus (from diagram)

Answer 5

• Protein coat
• Spikes (for attaching to specific cell surfaces)
• Nucleic acid (genetic code - DNA or RNA)

Question 6

Name 3 key features of a model bacterium (from diagram)

Answer 6

• Ribosomes (smaller than human ribosomes)
• Plasmids (smaller circles of DNA - transferable DNA)
• Capsule and cell wall (polysaccharide molecules - immunogenic)

Question 7

List the 3 bacterial shapes (2 main ones)

Answer 7

• Coccus (round)
• Bacillus (rod)
• Spirillus (very few with clinical importance!)

Question 8

List the 2 ways coccus bacterial are arranged

Answer 8

• Clusters

- Chains

Question 9

Outline the differences between gram positive and gram negative bacteria

Answer 9

Gram positive:

• Purple stain is retained = appears purple
• No outer membrane of lipopolysaccharide
• Primarily exudes exotoxins
• Thick outer peptidoglycan layer (multilayered)

Gram negative:

• Purple stain is NOT retained
• Lipopolysaccharide outer membrane
• Primarily exudes endotoxins
• Only thin peptidoglycan layer (single layered)

Question 10

Name some virulence factors (promote bacteria) and outline the 2 types of toxins

Answer 10

Virulence factors:

• Host entry (e.g. polysaccharide capsule)
• Adherence to host cells (e.g. fimbriae)
• Invasiveness (e.g. enzymes)
• Iron sequestration (siderophores)

Toxins:

• Exotoxins
• Endotoxins

Question 11

Name the 2 types of fungi - give 2 examples of each

Answer 11

Yeasts - single celled

e. g. Candida albicans (thrush)
e. g. Cryptococcus neoformans

Moulds - multicelled

e. g. Aspergillus species
e. g. Dermatophytes (ringworm/athletes foot)

Question 12

Name the 2 types of parasites - give 2 examples of each

Answer 12

Protozoa - single celled

e. g. Giardia lamblia
e. g. Plasmodium falciparum

Helminths - multicelled or worms

e. g. Roundworms
e. g. Tapeworms