Pathogens

Question 1

pathogen, opportunistic Define:

• Pathogen
• Chronicity
• Opportunistic pathogen
• Persistence/latency
• Virulence
• Virulence factors
• Pathogenicity islands

Answer 1

• Pathogen: a microbe capable of causing damage in the host
• Chronicity: persistence but with continued host damage over time
• Opportunistic pathogen: a microbe that causes damage/ disease only when host defences are weakened
• Persistence/ latency: failure of a host to eliminate a micro-organism. Usually opportunistic pathogens
• Virulence: the degree to which a pathogen causes damage, and how long they can survive outside of host
• Virulence factors: physical or chemical characteristics of a pathogen which contributes to the disease- causing process
• Pathogenicity islands: a group of genes encoding for virulence factors that can be transferred between bacteria

Question 2

What are the routes of transmission of microorganisms?

Answer 2

Indirect 
• Food
• Water
• Biological products
• Airborne
• Contacting objects
• Vectors like mosquitos (not infected, just carries)

Direct
• Vertical contact: mother to foetus/ child (between generations)
• Horizontal contact: kissing, patow, biting
• Vectors e.g. rabies (dog for e.g. is carrying the rabies disease)

Question 3

List the stages of infection process

Answer 3

1. Adherence and colonisation
2. Invasion
3. Immuno-evasion
4. Toxins
5. Replication
6. Bystander host damage

Question 4

Describe the stages of the infection process

Answer 4

1. Adherence and colonisation
   • Adhere and enter into host cells/ tissue
   • Can latch onto host through fimbriae, capsules, surface receptors
2. Invasion
   • Actively or passively penetrate through the mucous membrane or epithelium
   • Can invade through lysins, proteases (breakdown proteins like tight junctions in epithelial cells)
3. Immuno-evasion
   • Bacteria immuno-evades through proteases, capsules, biofilm formation, fibrinolysis, coagulase, leukocidins (kill leukocytes)
4. Toxins (optional)
   • Are substances which alter the normal metabolism of host cells with perilous effects on host
   • Exotoxins: heat sensitive proteins released by growing bacteria. Usually Gram +. Antibodies can bind and inactivate exotoxins
   • Endotoxins: LPS, from Gram - bacteria. Heat stable, and it works by disrupting the host protein cascade systems
5. Replication
   • They replicate and proliferate within the host
   • Virulence factors such as haemolysing, haemoglobinase to bind iron and gain energy to replicate
6. Bystander host damage (optional)
   • Damage is caused by an excessive immune response to infections
   • Chronic infection leads to chronic inflammation = periodontal disease