pathogenesis

Question 1

symbiote vs host

Answer 1

Symbiote = small organism
host = larger organism

Question 2

microbiota

Answer 2

total microbial population of a given site

Question 3

microbiome

Answer 3

genetic content of microbiota

Question 4

gut-brain axis

Answer 4

relationship between gut bacteria and enteric nervous system and how signals interact with the central nervous system
- by changing diet, metabolism can be modulated, gastro homeostasis, modulate reactions to stress

Question 5

importance of microbiota

physical barriers

Answer 5

physical barrier from exogenous pathogens via coating outer surfaces or secrete antimicrobial substances

Question 6

dysbiosis

Answer 6

disruption to normal microbiota
○ Change relative ratios that lead to infection
○ If immune system not sufficient to block infection process it leads to damage to host tissue (disease), manifests as symptoms

Question 7

pathogenesis

Answer 7

process whereby an organism cause disease

- Ex. Pathogen colonisers gut mucosal surface causing an inflammatory response leading to cellular and tissue damage

Question 8

exogenous pathogen

Answer 8

comes from external environment

Question 9

mutualism

Answer 9

Two independent organisms living together to their mutual benefit
- Bacteria in the colon
Further breakdown of 
undigested carbs - 
additional nutrients to

Question 10

commensalism

Answer 10

One organism benefits (usually microbe) while the other is unharmed (usually host)

Act as residents
Have the benefit of being present and grow as a community without harm
In the mouth
Benefit from food source while no harm to human

Question 11

parasitism

Answer 11

Where one organism (microbe) benefits at the expense of the other (human host)
Now accepted to view host - pathogen interactions as parasitic as the benefit is to the parasite

Microparasite
Viral, bacterial, protozoal, fungal pathogens

Macro parasite
Helminth pathogens

Question 12

what does the composition of microbes depend on

Answer 12

pH, temp, oxygen, water, nutrients

Question 13

skin

Answer 13

- strong structural barrier
Microbes will vary due to:
	- Inhospitable environment
		○ High salt 
		○ Slightly acidic
		○ Low in moisture
	- Moisture level
	- Amount of oxygen
Inhibitory substances
	- Lysozymes, antimicrobial peptides
Major inhabitants
Staphylococcus epidermis

Question 14

mouth

Answer 14

• Lots of different species of bacteria including anaerobes
  
  • Also anaerobic archea
  • Entry point for bacteria to colonise the URT
  • Saliva and food contain nutrients for organisms to grow
• Saliva produces antibacterial substances such as lysozyme to stint microbial growth

Question 15

nose

Answer 15

• normal microbiota found in the nostrils at the nares
  
  • Nasal mucus contain lysozyme
  • Most common bacteria found in the nose are the staphylococcus spp.

Question 16

lungs

Answer 16

○ In healthy individual

Very little microbiota present

Due to protective mechanisms to deal to with microorganisms to interfere with fine alveola

Question 17

protection from lung infection

Answer 17

□ Cells that line trachea produce mucus
Produced by Goblet cells in the epithelial lining
Trap microbes as they descend into the trachea

The lining of the trachea has cilia

Moves mucus in the direction to the mouth so it is swallowed into digestive system

Phagocytic action of alveolar macrophages mop up ant organisms

Question 18

stomach

Answer 18

○ Hostile environment for bacteria
○ Highly acidic
○ Barrier to intestinal tract
○ Microbial load drops
○ Gastric mucosa
○ Acid-tolerant Lactobacillus spp. And streptococcus spp.
○ Helicobacter pylori found in half the human pop.
§ Gastric ulcers
□ Can become a pathogen with changes to gastric lining

Question 19

small intestine

Answer 19

○ With distance from stomach
○ pH increases
○ Microbial load
○ Duodenum
○ Lightly colonised (<10^5 organisms/ml)
○ Jejunum
○ lightly colonised (<10^5 organisms/ml)
○ Ileum
○ Moderately colonised ((10^7 organisms/ml)
○ SI microbiota similar to colon microbiota as pH increases

Question 20

large intestine

Answer 20

dense with bacteria
anaerobic bacteria (oxygen deprived)

Question 21

UT

Answer 21

kidneys - sterile
urethra - washed out by urine
females have shorter urethra - increases likelihood of UTI

Question 22

vagina

Answer 22

pH varies with age

• slightly acidic in adult females
• neutral in prepubescents and menopausal

Question 23

4 steps of Koch’s postulate

Answer 23

1. Suspected pathogen must be present in every case and absent in healthy individuals
   
   2. Suspected pathogen must be isolated and grown in pure culture
   3. Isolate agent from pure culture must cause disease in new host
   4. The pathogen when re-isolated must present the same as it did in 2

Question 24

Limitations of Koch’s postulate

Answer 24

• No host factors taken into account
  
  • Have to be able to culture organism
  • Organism can lose virulence in lab
    Requires animal model

Question 25

Endogenous agent

Answer 25

normal microbiota cause disease

Question 26

Opportunistic

Answer 26

• cause disease only under predisposing circumstances both endogenous and exogenous
  
  • Endogenous
    ○ Occupy different surfaces
    ○ Disseminate through perforation
    ○ Change in ecological niche - lack of competition
  • Exogenous
    ○ Immunocompromised
    ○ Nosocomial infection

Question 27

primary pathogen

Answer 27

• Cause disease in healthy host
  
  • Overcome host defences
  • Growth and spread
  • Cause cell damage
    Spread to other hosts

Question 28

sources of primary pathogen

Answer 28

• Respiratory
  
  • Faecal-oral
  • Sex
  • Vector
  • Zoonosis
    Vector- vertebrate

Question 29

iceberg concept

Answer 29

• Mostly asymptomatic- carriers
  
  • Acute
    ○ Incubatory - not yet ill
    ○ Convalescent - developed disease and recovered
  • Chronic
    Harbour pathogen for long period

Question 30

change in diseases

Answer 30

• Reduction in communicable disease

Most causes of death in low income countries are communicable disease