Microbiology - Lecture Thirty Two : Microbial Pathogenicity
5 important questions on Microbiology - Lecture Thirty Two : Microbial Pathogenicity
What are some examples of Medically Important Pathogens ?
- Viruses: H1N1 Influenza Virus (Single Stranded RNA Enveloped)
- Fungi: Trichophyton spp.
- Prions: Kuru
- Protozoa: Plasmodium spp. (Malaria parasites).
- Helminths: Ancylostoma duodenale (Hook worm)
- Bacteria: Bacillus anthracis (Gram Positive endospore forming, rod shaped bacterium)
What are Koch's Postulates ?
- The bacteria must be present in every case of the disease
- The bacteria must be isolated from the host with the disease and grown in pure culture
- The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
- The bacteria must be recoverable from the experimentally infected host
- Some microbes cannot be cultured (eg. Treponema pallidum)
- Some pathogens can also be found in healthy subjects
What are the key stages of Microbial Pathogenesis?
- Adheres to the host cells
- Invasion of host tissues
- Replication within host tissues
- Disease causing damage to host tissues (pathology)
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What are the broad classes of bacterial virulence factors ?
- Fimbriae
- Motility (Flagella)
- Siderophore (binding iron in low iron conditions)
- Capsules (stops WBC from phagocytosing them)
- Toxins
What are the definitions of Endotoxins and Exotoxins?
- Lipid portions of lipopolysaccharides (LPSs) that are part of the outer membrane of the cell wall of gram-negative bacteria. The endotoxins are liberated when the bacteria die and the cell wall breaks apart.
- Proteins produced inside pathogenic bacteria, most commonly gram-positive bacteria, as part of their growth and metabolism. The exotoxins are then secreted or released into the surrounding medium following lysis.
These are produced within living bacteria and released when they are alive :
- CYTOTOXINS : Cause beta haemolysis of red blood cells
- NEUROTOXINS : Causes paralysis. Stops neurotransmitters from being released
- ENTEROTOXIN : Causes severe dysentery
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