pathogenesis Flashcards
symbiote vs host
Symbiote = small organism host = larger organism
microbiota
total microbial population of a given site
microbiome
genetic content of microbiota
gut-brain axis
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
importance of microbiota
physical barriers
physical barrier from exogenous pathogens via coating outer surfaces or secrete antimicrobial substances
dysbiosis
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
pathogenesis
process whereby an organism cause disease
- Ex. Pathogen colonisers gut mucosal surface causing an inflammatory response leading to cellular and tissue damage
exogenous pathogen
comes from external environment
mutualism
Two independent organisms living together to their mutual benefit - Bacteria in the colon Further breakdown of undigested carbs - additional nutrients to
commensalism
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
parasitism
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
what does the composition of microbes depend on
pH, temp, oxygen, water, nutrients
skin
- 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
mouth
- 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
nose
- normal microbiota found in the nostrils at the nares
- Nasal mucus contain lysozyme
- Most common bacteria found in the nose are the staphylococcus spp.
lungs
○ In healthy individual
Very little microbiota present
Due to protective mechanisms to deal to with microorganisms to interfere with fine alveola
protection from lung infection
□ 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
stomach
○ 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
small intestine
○ 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
large intestine
dense with bacteria anaerobic bacteria (oxygen deprived)
UT
kidneys - sterile
urethra - washed out by urine
females have shorter urethra - increases likelihood of UTI
vagina
pH varies with age
- slightly acidic in adult females
- neutral in prepubescents and menopausal
4 steps of Koch’s postulate
- Suspected pathogen must be present in every case and absent in healthy individuals
- Suspected pathogen must be isolated and grown in pure culture
- Isolate agent from pure culture must cause disease in new host
- The pathogen when re-isolated must present the same as it did in 2
Limitations of Koch’s postulate
- No host factors taken into account
- Have to be able to culture organism
- Organism can lose virulence in lab
Requires animal model
Endogenous agent
normal microbiota cause disease
Opportunistic
- 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
- Endogenous
primary pathogen
- Cause disease in healthy host
- Overcome host defences
- Growth and spread
- Cause cell damage
Spread to other hosts
sources of primary pathogen
- Respiratory
- Faecal-oral
- Sex
- Vector
- Zoonosis
Vector- vertebrate
iceberg concept
- Mostly asymptomatic- carriers
- Acute
○ Incubatory - not yet ill
○ Convalescent - developed disease and recovered - Chronic
Harbour pathogen for long period
- Acute
change in diseases
- Reduction in communicable disease
Most causes of death in low income countries are communicable disease
